INTRODUCTION:
The aquarium nitrogen cycle is simply put the method by which fish wastes and other decomposing organic matter (such as uneaten fish food) is converted from Ammonia or Ammonium to nitrites to nitrates which are then either converted to free nitrogen (which is a gas that will not remain in the water) by plants or de-nitrifying anaerobic bacteria OR you remove/lower your nitrates by way of regular water changes.
Without this process going on in your aquarium/pond the keeping of fish or other inhabitants would be nearly impossible as ammonia is highly toxic in even small quantities (ammonium is not, but is quickly converted to ammonia at higher pH), nitrites are also toxic although not as much as ammonia. Nitrates are not toxic to most freshwater fish except in high amounts with long term exposure (this is not the case for many saltwater inhabitants though).
So with this in mind it is important to have an “established aquarium nitrogen cycle” in your aquarium or pond.
What is nitrogen?
Nitrogen is an element vital to all life processes on Earth. Nitrogen is very important in our biosphere, where nitrogen comprises 78% of the atmosphere, and is part of every living tissue. It is a component of amino acids, proteins and nucleic acids. With the exception of carbon, nitrogen is the most universal element of life. Life could not exist without nitrogen. Nitrogen is essential for organic development; nitrogenous compounds are also required by some organisms for metabolic functions and respiration.
All living organisms, from fish to plants, have great quantities of assimilated nitrogen in their tissues. Nitrogen is a fundamental ingredient for the formation of proteins and nucleic acids. Every organism you place in your aquarium adds nitrogen based compounds; from fish to coral, to live rock, to plants.
The introduction of food also adds nitrogen. Dead or alive, they are organic masses, and possess the same nitrogenous attributes as the fish, plants, invertebrates you added to your aquarium.
Inorganic nitrogen is added two ways: the atmosphere and new water. Atmospheric nitrogen (N2) is incorporated into our aquarium water by way of nitrogen fixing bacteria and by Cyanobacteria (bacteria that obtain their energy through photosynthesis) as ammonia (NH3). Some Cyanobacteria fix nitrogen gas, which cannot be used by plants, into ammonia (NH3), nitrites (NO2â) or nitrates (NO3â). Nitrates can then be utilized by plants and converted to nucleic acids and protein.
Inorganic nitrogenous compounds from our tap or well water also enter our aquarium, often as Nitrates or Nitrates. Reverse Osmosis can remove much of this. For more about tap water, please see this article: “What should I know about tap water for my aquarium? From Chlorine and Chloramines to Phosphates”
NITRIFICATION:
When an organism dies, nitrogen is moved from plant or animal into the inorganic chemical ammonia by the process of bacterial decay. Ammonia is also produced by bacteria in the breakdown of protein. This process is called Mineralization and is the end result of the metabolism of food. However, ammonia is produced from both metabolism and mineralization. The decomposition (mineralization) process produces large quantities of ammonia (NH3) through the process of ammoniafication. Heterotrophic microbes (organisms that require organic substrates to get its carbon for their growth and development) utilize the organic compounds of decomposing matter as their carbon source. Ammonia (NH3) is the byproduct of this consumption.
Ammonia, in its neutral state, exists as ammonium (NH4+). Ammonium (NH4) is formed by the protonation (the addition of a Proton (H+) to the molecule. During this process of protonation NH3 (which is a base) converts into a weak acid (an acid which has the tendency to lose, or "donate" a hydrogen ion, also known as a “Brønsted-Lowry acid”. This tendency to “donate” a hydrogen ion is how NH4 converts back to NH3 as pH rises. Products such as Prime block this process, maintaining the extra hydrogen ion
Ammonia is assimilated in more than one way. Plants (such as Hornwort) and algae can assimilate ammonia and ammonium directly for the biosynthesis. The remaining bulk of decomposed byproducts are utilized by bacteria in a process called nitrification. Ammonia does not last long in a healthy aquarium environment, fortunately. Nitrifying bacteria such as Nitrosomonas quickly break down ammonia into less toxic Nitrite (NO2). During this process, specific species of nitrifying bacteria strip the ammonium of its hydrogen molecules as an energy source. Oxygen molecules are then affixed to the stripped nitrogen, forming the oxide nitrite (NO2).
Another group of bacteria (Nitrobacter ) utilize the enzyme nitrite oxidase that is then responsible for converting nitrite into nitrate (NO3). This nitrate can either be used by plants as a nutrient source, or can be further broken down into nitrogen gas (N2) through the activity of anaerobic bacteria such as Pseudomonas .
It should be noted, that without oxygen (nitrification is an oxidative process), none of this process can take place.
What are nitrifying bacteria?
There's a lot of confusion among aquarists about nitrifying bacteria. This is due in large part to the recent emergence of a wide variety of bacterial products claiming to be nitrifying aids. Most of these products actually contain species of heterotrophic bacteria from the genera Bacillus, Pseudomonas, Escherichia, and others.
True nitrifying (Autotrophic) bacteria are considered to be those belonging to the family Nitrobacteraceae whose energy sources are derived from the chemical conversion of ammonia to nitrite, or, nitrite to nitrate (Autotrophic bacteria are organisms that produce complex organic compounds from simple inorganic molecules). They require oxygen, utilize mostly inorganic (without carbon) compounds as their energy source, and require carbon dioxide (CO2) for their source of carbon. In the case of the Nitrobacteraceae these energy sources are derived from the chemical conversion of ammonia to nitrite, or, nitrite to nitrate.
These bacteria are primarily gram POSITIVE, which is why you need to be careful when treating with medications that are primarily gram positive such as Erythromycin (Maracyn), Ampicillin, or Penicillin (I have also found Tetracycline Hydrochloride to be hard on nitrifying bacteria as well). Another point of misinformation about these bacteria since they are gram positive is that most aquarium diseases are gram negative (especially marine) such as Vibrio, Columnaris, Pseudomonas, Aeromonas and treatment with antibiotics such as Kanamycin or Nitrofurazone which are primarily gram negative will NOT interfere with the nitrifying cycling process.
Five genera are generally accepted as ammonia-oxidizers and four genera as nitrite-oxidizers. Of these, Nitrosomonas (FW), Nitrosococcus (SW), and Nitrospira (ammonia-oxidizers); Nitrococcus (SW), Nitrobacter (FW), and Nitrospina (nitrite-oxidizers) are the most important. Species of marine nitrifying bacteria are different from those that prefer fresh water, and yet, are very closely related.
Heterotrophic Bacteria (which are generally found in most over the counter aquarium cycling products due to their portability) are usually aerobic, they can be either gram-positive (ex: Bacillus) or gram-negative (ex: Pseudomonas), heterotrophs (an organism that requires organic substrates to get its carbon for growth and development). Some are strictly aerobic, but many are facultative anaerobes (they can survive in both the presence or absence of oxygen). Another point is growth (which is why Heterotrophic bacteria are favored for cycling products); nitrifying (Autotrophic) bacteria will double in population every 15-24 hours under optimal growth conditions. Heterotrophic bacteria, on the other hand, can reproduce in as little as 15 minutes to 1 hour.
Unfortunately research has shown that up to one million times more of these heterotrophic bacteria are required to perform a comparable level of ammonia conversion that is attained by true autotrophic nitrifying bacteria, in part due to the fact of Heterotrophic Bacteria to convert many organics into food.
References: autotroph , Cloudiness in the Water, & What are bacteria?
A few key points about ammonia:
• Ammonia in the form of toxic NH3 commonly found in aquariums from wastes
(Animal and plant) will convert to NH4 (which is much less toxic) in a pH of around 6.4 or less.
• Surface agitation can cause some ammonia ions to evaporate, but not quickly enough to be significant to a healthy aquarium. The ammonia commonly found in aquariums should not be confused with ammonia carbonate used in cooking which more readily evaporates nor should an aquarist confuse the process of evaporation in a cooling system commonly used in RV refrigerators which heats the ammonia for evaporation and cooling (this system basically works by heating anhydrous ammonia to evaporate it then the ammonia condenses and cools and the process starts over again).
• Toxic NH3 ammonia can be remove or detoxified by products such as Prime , Ammo Lock, or Amquel but this is a short term solution to proper bio filtration.
DENITRIFICATION:
Is the process of converting Nitrates (NO3) in to Nitrogen (N2), which is dispersed into the atmosphere. This process can take place in an environment without oxygen by anaerobic bacteria. This process is more common in Marine aquaria and takes place in fine #00 sand, , live rock, or “aquarium mud”. In freshwater aquariums this process often produces deadly Hydrogen Sulfide, but by maintaining an oxygen level above 1 ppm, this can be avoided. Plants roots are great for maintaining this balance of oxygen in the gravel for proper Nitrate removal.
A system of plates (similar to an UGF) or pvc utilizing a "void space" called a plenum is often used for Nitrate removal in Saltwater and freshwater aquariums. These are not to be confused with under gravel filters.
There are different styles of plenums. The basic structure of the plenum system is a 3" to 4" layer of sand, suspended 2" to 3" above the bottom of an aquarium. A basic plenum may be created by suspending egg crate material or under gravel filter plates above the aquarium bottom, using inert supports such as PVC pipe. I prefer to use pvc pipe with slots cut in the bottom and joined to form a grid on the bottom
I do not recommend Plenums for marine aquariums as I have not found them effective and in fact this recent scientific experiment backs this up:
Saltwater Plenum
BIOFILTRATION:
Nature can pack a lot of bacteria into small places, which is to the advantage of the aquarist. For bacterial growth, all that is required is ammonia and oxygenated water. This is the beginning of the nitrogen process and the growth of bacterial colonies.
Remember you need oxygen and a lot of surface area for bacterial colonies. Wet/dry filters, sponge filters, ceramic media, and loosely packed upper layers of gravel are all sources for bacterial accumulation. If there is not adequate surface area in oxygen areas of the filter media or gravel, nitrification will be poor. Relatively new scientific evidence shows nitrifying bacteria to be sticky and adheres to the surfaces like glue, so agitation of filter media when rinsing (no tap water), or vacuuming of gravel will not destroy these colonies. This is why water exchanges with established aquariums usually are ineffective for cycling aquariums and why the myth of UV Sterilizers killing beneficial bacteria is just that, a myth.
Water will follow the path of least resistance, so if your filter or gravel has a build-up of non-nitrifying bacterial slime or is packed to tightly, nitrification will not be achieved. Sponge Filters or Pre-Filters are an inexpensive filter medium for colonies of nitrifying bacteria. Wet/dry filters and live rock (in Marine Aquariums) are excellent sources of bio filtration in larger aquaria. Bio-Wheels are very popular, but in my tests in my maintenance business they are VASTLY overrated. They tend to accumulate hard water deposits and stop and even when they are working my tests have shown little difference in aquariums when they are removed as compared to sponge filters or wet/dry filters. Canister filters are also good sources for nitrification as long as the proper media is used (such as ceramic rings) and the media is not packed too tight and is rinsed regularly.
SUMMARY OF LEVELS;
In healthy aquarium ammonia and nitrites should be at 0 ppm
In a healthy freshwater aquarium Nitrates should be 15-50 ppm (below 15 ppm is not healthy for planted freshwater aquariums).
In a healthy Saltwater fish aquarium nitrates should be below 40 ppm.
In a healthy Marine Reef aquarium nitrates should be below 20 ppm (or even less, many reef keepers aim for less than 10 ppm).
METHODS OF AQUARIUM CYCLING:
All the methods I will describe below are versions of “FISHLESS CYCLING”. Many associate fishless cycling with the pure ammonia method, however fishless cycling is ANY method that does not introduce fish until the aquarium has gone thru the nitrogen cycle, in other words, the ammonia and nitrites have gone up then back down which can take from 10 to as long as 45 days depending on method tank size and temperature. I will note that method one (if done properly) rarely results in an ammonia and nitrite spike, this is why it is my preferred method WHEN possible (which often it is not).
I do NOT recommend adding “starter” or cycling fish to start your nitrogen cycle for either freshwater or saltwater.
[1] My preferred cycling method is to transfer filter media (sponges work best, although floss, ceramic media ect. are also fine) from an established aquarium and possibly along with some gravel, then introduce the fish SLOWLY after 5-7 days. The method of adding “aged” media is much faster (you still have to take it slow), and provides all the necessary bacteria, the only negative is adding disease pathogens to your aquarium, but I have rarely encountered this problem. To prevent this transfer of disease pathogens and parasites, only use a media source where no new fish have been added in 30 days, ALL water parameters are good, and if possible has UV Sterilization (although not necessary).
For marine tanks the use of seasoned or “cured” live rock serve this purpose quite well.
I recommend this method even more with Marine tanks using seasoned (cured) live rock and/or live sand as well as filter media. In Marine tanks I still prefer to added aged media (not essential, but still better) along with 1-2 lbs (2.2 -4.4 kg) CURED live rock per gallon (approx. 4 liters).
This method will give you more instant bio bacterial colonies and this is method that is used by far the most by the professional aquarium maintenance community (which needs faster more sure results for their clients), despite the internet popularity of the next two cycling methods.
Also keep in mind that many pathogens such as pseudomonas are usually present in a healthy aquarium, but when fish are stressed, the fish are in poor health due to poor feeding and lack of proper minerals, and/or water conditions are less than desirable- these pathogens will be opportunistic and cause a disease in the fish.
We used this method for our Aquarium Maintenance route for years and never lost a fish to Ammonia or nitrite poisoning, and disease transfer was minimal.
Another product that does not necessarily help speed up the cycling process itself, but de-toxifies the ammonia and nitrites during this process, allowing for less stress on fish is "Prime"
[2] Another method is fishless cycling where un-scented pure ammonia is poured into the aquarium (3-5 drops per gallon pure ammonia or 1-2 teaspoons per 10 gallons) so as to bring your ammonia level to 3-4 ppm. Then it takes about 2-6 weeks (usually about 3 weeks) for the aquarium to cycle (when your ammonia and nitrites have dropped to 0).
Although this method is growing in popularity, I do not recommend it for a few reasons, not because it does not work (it does);
*This method does not add actual bacteria (and is not really any quicker than the method below: adding fish food to a fishless aquarium) and because human nature is to want to add fish sooner than the 2-6 weeks it takes for this method.
*It is still not as quick as my preferred method above (seeded media, gravel, sand, live rock).
*This method is especially dangerous when used with live rock and/or sand that has already been added as the ammonia will kill me organisms that reside in live rock adding even more ammonia and pollution to your tank thus defeating the reason for this method.
[3] Another method is the gradual addition of fish food to an otherwise empty aquarium (no fish). This can be a very effective means of cycling that is preferred by many experienced aquarists. This method takes about the same time as the pure ammonia method (2-6 weeks, usually about 3).
This is my preferred method when aged bio media is not available (not everyone has a friend or helpful local fish store to give them some aged media).
4 ppm is a typical fishless cycling target whether using the fish food method or ammonia. Higher (7 ppm) or lower (3 ppm) is also fine for healthy bacterial colony growth (based on mine and others in the maintenance community’s experience).
Regardless of fishless cycling method chosen, the bio load is always going to be in flux (higher or lower). When higher is needed, nitrifying bacteria double in population in 18 to 24 hours. When less are needed, they die back and are consumed by each other.
The method of adding “aged” media is much faster (you still have to take it slow), and provides all the necessary bacteria, the only negative is adding disease pathogens to your aquarium, but I have rarely encountered this problem. Keep in mind as discussed earlier, because nitrifying bacteria adhere to surfaces like glue, aged aquarium water is ineffective for cycling, but it can be useful for proper water nutrient levels in a new
aquarium.
[4] There are many products for cycling available too, but most in my opinion do not work well although properly cared for BioSpira is may be effective (the key is properly cared for, the shelf life is short and it should be stored between 34 F and 40 F). I will note however that many I know in the aquatic community such as other in aquarium maintenance and in a forum have not had all that good of results in tests (my own experience with this product is limited to once with no scientific controls in place).
This is in part (IMO) due to the fact that aerobic nitrifying bacteria cling to media and gravel (this has been PROVEN scientifically) and do not work while suspended in water. Also poor storage and shelf life undoubtedly play a role as well.
It should also be noted that freshwater products CANNOT be used in saltwater or vice versa. Some companies make products from the proper Autotrophic that contain the correct freshwater or saltwater bacteria (these must be refrigerated). Fritz-Zyme # 7 or #9 are good examples.
Liquid Cycle and Stress-Zyme are just preserved bacteria that are more useful for over feeding or other bio over loads in an established aquarium (as aerobic bacteria needed for nitrification do not store well in liquid form at room temperature without oxygen). Even Fritz-Zyme which contains the proper nitrifying autotrophic bacteria tends to use it’s in bottle food supply and be less effective.
*For marine aquariums I would point out that live sand does not add nitrifying bacteria nearly as well as live rock due to the fact of oxygen depth penetration.
Also the use of “live saltwater” is NOT based in any real scientific evidence since nitrifying bacteria secrete glue like substance to adhere to substances such as live rock and are generally not found in real quantity in the water column.
*Finally I will note as to different cycling methods; I have used these different methods in my Aquarium maintenance and research business in controlled tests and still found that the added media/sand/gravel/seasoned live rock method works fastest and with the best results, although I have also had good results with this method combined with the fish food method (do not combine with the pure ammonia method)
*Effect of plants on Aquarium Cycling:
As mentioned earlier, many plants also remove nitrogenous waste such as Hornwort. I usually do not add all the plants I desire until the aquarium is fully cycled (regardless of method used), which is usually 2-3 weeks. The plants will help carry the waste load vs. an aquarium without plants, but I like to see at least some bacteria establish it self before a full load of plants are added. Having plants in the beginning does help keep the dangers of ammonia (NH3) or Nitrites (NO2) from building to toxic levels, which allows for a quicker addition of fish to your aquarium.
Summary:
Please note that whatever method you choose to cycle your aquarium from aged media, to pure ammonia, to Bio Spira; that if your fish are exposed to high ammonia and nitrites for any prolonged period (over 24 hours in my opinion), these fish can and will suffer permanent gill damage that will cause future problems with disease resistance and even overall aquarium health as these fish may become a starting point for opportunistic infections.
A FEW DOS AND DONTS FOR MAINTAINING A HEALTHY NITROGEN CYCLE:
*Do Rinse filter media in used tank water or de-chlorinated tap water so as to not kill nitrifying bacteria.
*Do NOT rinse your filter media in tap water or turn filters on and off, this will hamper the establishment of healthy bio colonies of nitrifying bacteria. Filters should run 24/7 except in rare instances.
*Do NOT wash gravel or totally change water, again this will destroy or hamper establishment of bio bacterial colonies.
*Do rotate filter media changes so as to always have older media with bacterial colonies. In a HOB filter with a cartridge, place a second cartridge in 7-10 days before changing the old one of install a sponge pre-filter on your HOB filter such as a Filter-Max Pre-Filter
*Do add de-chlorinators when changing water over 10%
*Do NOT vacuum ‘dead’ spots under live rock in the live sand of a Marine Tank ONLY. (This can destroy anaerobic bacterial colonies in Marine Tanks needed for de-nitrification). Even then try and vacuum only the top layer in open areas of live sand in marine tanks.
WHAT TO DO FOR HIGH AMMONIA OR NITRITES:
*Change anywhere from 30%- 50% water per day until you at least reach an ammonia or nitrite level of 2 ppm or less (0 is what you want eventually).
*Use Prime (removes chlorine/chloramines, detoxifies ammonia & nitrite) or any other Ammonia/Nitrite de-toxifier such Ammo Lock, Amquel Plus or Amquel. These products do not remove ammonia they change the ammonia from highly toxic NH3 to less toxic Ammonium (NH4). Please note the ammonia will still test after using these products as the test kits do not differentiate between ammonia and ammonium (ionized ammonia). Prime will keep the ammonium safely “bound” even if the pH climbs (which would otherwise convert NH4 to NH3). The ammonium is still available for nitrifying bacteria to consume and therefore Prime will not interrupt the growth of healthy bio-bacterial colonies as the ionized ammonia and nitrites are still available for nitrifying bacteria. It should be also noted that most test kit will still show the ammonia/nitrites at the SAME level as before the addition of Prime/Amquel +, however rest assured this is in a non-toxic ionized form that is still bio available to Nitrobacteraceae bacteria that forming in your filter media/gravel.
Here is more information about Prime: “The detoxification of nitrite and nitrate by Prime (when used at elevated levels) is not well understood from a mechanistic standpoint. The most likely explanation is that the nitrite and nitrate is removed in a manner similar to the way ammonia is removed; i.e. it is bound and held in a inert state until such time that bacteria in the biological filter are able to take a hold of it, break it apart and use it. Two other possible scenarios are reduction to nitrogen (N2) gas or conversion into a benign organic nitrogen compound”.
See SeaChem Support AND
"Aquarium Answers: Aquatic Water Conditioners" for more information.
*Add salt (NaCl); this is a popular method for “nitrite poisoning” and should be added at 1 tablespoon per 5 gallons to 1 teaspoon per gallon depending upon fish sensitivities. The addition of salt will prevent methemoglobin that forms in the blood due to nitrite exposure from building up.
Salt can be combined with Prime or Amquel Plus, however from my experience the salt method is not nearly as effective as Prime when used by itself.
*For high ammonia or nitrite exposure (common in fish shipped from long distances), the use of Methylene Blue in 30 minute baths is very effective and also counters the effects of methemoglobin in the blood by increasing the hemoglobin oxygen carrying abilities.
*Consider zeolite in the filters to absorb some of the ammonia (FRESHWATER ONLY!).
*Add "seasoned" by bio media such as sponge or filter fiber form another healthy tank to kick start your bio filtration.
*Cut back on feeding and do not use fish foods high in non aquatic proteins, which are mostly un-digestible and add to your ammonia.
For more about proper fish food ingredients, please see this article: Quality Fish Food; what ingredients are needed for proper fish nutrition, growth and health.
WHAT TO DO FOR HIGH NITRATES:
Although not generally toxic high nitrates can stunt fish growth and lead to health issues if fish are exposed to high nitrates for an extended time in freshwater. In saltwater the same holds true for fish, but with many invertebrates, especially coral and cephalopods nitrates above 20 ppm can be deadly.
*Prime as well as Amquel Plus will neutralize the Nitrate but is not a long term solution to high nitrate problems.
*Perform a water change using a gravel vacuum to remove not just dirty water, but “mulm” that will decompose and enter the nitrogen cycle and eventually become nitrates.
This can be a particular problem with Under Gravel Filters (UGF), decomposing organic debris will tend to build up under the filter plate. For these filters I recommend occasionally removing the lift tubes and placing a siphon into the opening and removing as much organic debris (mulm) as possible.
Even without UGF, poor vacuuming procedures (or none at all) can contribute to high to high nitrates. Make sure and vacuum around and under ornaments as well, although be careful around live plants. I think the Aquarium Cleaning Machine (Aquarium power siphon and re-circulating micron filter is a better idea for larger aquariums.
*Proper filtration and maintenance; Make sure and regularly rinse in de-chlorinated or used aquarium water (never tap water) your bio filter media. This includes bio rings and balls commonly found in wet dry filters and canister filters, sponge filters, bio wheels, or any other media that is not changed in the filter. This is especially important with filters that tend to become “nitrate factories”, which include in my experience (AND tests) to be; Canister Filters, Wet-Dry filters, and Emperor Filters. This is not to say these filters are bad, it is just important to not ignore properly cleaning these filters even though their large capacity makes it very easy to do.
I will however add that for reef aquariums I do not recommend the before mentioned filters unless one substitutes live rock crumbles (or volcanic rock) for bio balls.
The reason behind this is that bio balls although excellent for aerobic nitrification only contain bacteria on the outer surfaces and thus are NOT capable of sustaining anaerobic de-nitrifying bacteria necessary for nitrate removal as these bacteria live on surfaces where little oxygen penetrates. Live Rock crumbles/scrap are capable of containing these bacteria necessary deep inside their pores (as is volcanic rock, although not quite to the same level, but close)
I have seen nitrates in freshwater go down by simply changing filter systems (the over all health of the aquarium improved as well). The last time I did this was by removing an Emperor 400 and replacing it with a combinations Sponge filter/ Internal filter/ Fluidized Filter System.
*Add aquatic plants to freshwater especially hornwort.
For saltwater some green algae will perform this task as well (this is why I do not remove all my green algae in the marine aquariums I maintain). Caulerpa Algae (which looks like a plant performs nitrate removal reasonably well).
*For saltwater aquariums consider a Refugium or a Protein Skimmer. A Refugium uses plants in a sump with strong lighting to remove nutrients including nitrates. Protein skimmers remove nitrates before they enter the nitrogen cycle via foam refraction (a similar idea to vacuuming the “mulm”). Personally I have used many a Protein Skimmer and find many over rated considering the constant adjustments in many of the Skimmers available, rate of refraction compared to water volume. However this is not to say a protein skimmer does not work, these are useful tools in marine aquariums for nitrate control, I just do not recommend “throwing all your eggs in one basket” with these devices. Also keep in mind that not all Protein Skimmers are created equal, so purchasing a true quality unit is worth the investment such as the V-2 Skim Professional Skimmer
A Mud Filter or Mud Filter/Refugium combination works well too.
*Besides the Refugium, a DSB (Deep Sand Bed) in a bucket works well. Put 8" to 12" of fresh, clean sand in a 5 gallon bucket; Oolitic sugar-fine aragonite works best in my opinion. Drill a bulkhead about an inch or two higher than the top of the substrate for the water to flow out from back into your tank/sump. A flow rate of 150-200 gph, just enough flow over the sand to keep solids in suspension, I recommend pre-filtering the water first to prevent detritus build up. This is a very effective method (similar to Mud Filters) that can bring Nitrates down to near 0.
Please see this link for a DIY Deep Sand Bucket/Tank picture and more information about this idea: “DIY Deep Sand Bucket”
*For saltwater aquariums I have observed lower nitrates with 175 watt 20,000 K Metal Halide lights
thee end.