Controlling Nitrates in a Saltwater Aquarium

Nitrates can kill every fish and coral you have in your tank if they aren’t kept in check.

The good news is that keeping them in check requires patience and using several nitrate reducing tools that I cover in this episode of Mr. Saltwater Tank TV.

Links in this video: Go Plus One: Bump it up a notch

NOTE: If you want to leave a comment, click on the “comment” link below the video.

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Comments for this article (84)

  • Here is where you leave comments! I’m interested in what you have to say!

  • Wesley Forbes says:

    Hello, it took some time but I use cheatomorpha (sp) in my sump with lights on 24 hours and my nitrates went from 10+ to 0.0. Again it did take some time but it did happen! I do not dose carbon, but I run activated carbon in a reactor and I also feel that helps due to removing organics in the water. Am I correct about that?

  • Wesley…good work on the cheato. Keep in mind that part of photosynthesis is the “dark cycle” so I’d advise to run your refugium lights for 12 hrs a day. You can also run your refugium lights opposite of your tank lights to help mitigate the pH drop at night.

    You are correct about activated carbon in the reactor. It removes organics and makes your water sparkly clean.

  • Ric Johnson says:

    Gee who was that good-looking talking head in that video?

  • Marc says:

    I use a sulfur denitrator. I feel this method is much more effiecient than cheato. I tried cheato and experienced zero benefit. Sulfur denitrators deserve more merit in this hobby due to it’s powerful capabilities. Thanks, Marc

  • rick says:

    Thanks for the video very useful for the beginner. Keep up the good work.

  • He looks familiar doesn’t he Ric?

  • Marc…how much cheato did you use and long did you try it out?

    Refugiums do take a while to get running such that there is enough macro algae to eat all the nitrates in the water.

  • You are welcome!

  • Nick Vento says:

    Thanks for all the great video tips man it really helps and I enjoy watching them, but my question is, Going +1 on your skimmer, would that mean like for a 100 gallon tank use a skimmer rated for 200 gallons? Thanks again for all the help

  • Paul says:

    Hi Mark,

    Thanks for another nice video. i would like to say that there is a “gold bullet”
    and that is to run an algae scrubber. See:
    Many already using it and have reported their results.

    My nitrates are 0 (zero), also my phosphates are zero. I have No skimmer, almost never do any water change. But do dose some adatives. The thing also removes heavy metals. I have no RO/DI unit, just a simple drinking water filter.

    I over sized my scrubber so i only need to clean it once every 2 weeks. Does requere some DIY skills to set it up.

    I have no bad algae or bacteria in my tank, but I do feed a lot.
    So no skimmer, rare water change, no RO/DI unit, so how is that for
    “Money in your pocket”?
    I guess this totaly reverse to your approach, love to hear your comments,
    or even a video on the subject from you.

    Thanks, and looking forward from more video’s.

  • Nick…yes. Use a skimmer that is rated 1 step higher than what you need.

    If you send me the specs on your tank, I can help you look at options.

  • Paul…I know of algae turf scrubbers. A friend of mine is running one on his 225G tank.

    I think they haven’t become mainstream due to the “DIY” aspect. To me, “DIY” = done in years. Most DIY projects never leave the ground or actually get finished.

    If a company made a good turf scrubber product and marketed it well, I think we’d see more of them.

    I do like the approach though and my next tank will have room to try it out.

    I’ll get in contact with my friend about filming his tank and scrubber

  • Nick Vento says:

    Well my tank is 100 gallon with a 30 long used as a sump/refugium, I have a ASM G2 skimmer now I’ve heard it was one of the old ones but I got it for free so cant complain about that right and it seems to pull out alot since I watched your video on tuning you skimmer, 150lbs of live rock that I used to cycle my tank as it was uncured it’s now 4 months old it took a month to get through the initial cycle, I have 6 inches of sand in the fuge and a 1.5 inches of crushed coral in the main tank, 2 damsels, 1 carpenter wrasse, 7 turbo’s and 7 hermits, no coral yet im letting my tank get alittle older till I start that but I cant wait, I would really like to try the algea scrubber but I dont have the room, im really into the DIY stuff though, well if theres anything i left out let me know

  • Marc M says:

    Hi Mark,

    To reply to your question, I used a 58 gallon tank and filled it up with 5 large pieces of cheato along with a 4 inch deep sand bed. I did give the cheato a chance and left it there for a period of a year. The cheato did not grow well even under 5500K lighting and 10,000K lighting without the use of actinics. My nitrates were still over 100 ppm and my PO4 was hovering around 0.2ppm. I was severely dissapointed and tore the refugium down. I them built a 36 inch tall sulfur denitrator and let it cycle for 4 weeks. After that my nitrates fell rapidly and in about as little as 3 weeks my nitrates were ZERO! Absolutly the best equipment I have ever built and owned! Fish are growing again because the previous levels stunted the growth of my fish. My Emperor is fully healed from HLLE which I believe was caused by high nitrate levels. Thanks, Marc

  • sos says:

    Love the videos.

    I wanted to make a suggestion for future videos as a follow up.

    Refugiums, Macro Algaes, bio pellets, zeovit system.

  • Andrew says:

    Hi Mark,

    Awesome video and of great help to a newbie to this hobby like me. This is somethiing that is driving me nuts as I don’t get anywhere close to the zero mark. My nitrates have always been around 10 for the last 4 months and it is hard to control. I am changing water (20%) every 2 weeks but I do think my issue may be that a “reef safe” Octozin I had to add may have smashed my bacteria – your thoughts on this? I was going to add another batch of “reef start” bacteria to boost. Otherwise everything is great in the tank.

    Even added pure-ichem (by seachem) to supposedly assist here. Bag is placed after the bio filter where the water runs through just before the return pump.

    Any other ideas?

  • Did you see a spike in nitrates after you added the Octozin?

    Adding the bacteria won’t hurt, just don’t go overboard since your tank is established.

    Tell me more about your “bio filter”…what are you referring to here?

  • Sos…good ideas. I’ve added them to my list of shows.
    Thanks for the suggestion

  • Marc…cheato is very popular and sometimes doesn’t do much like you described. I have some in my fuge but it always withers away and i’ve switched to calupera and that stuff grows strong.

    Glad the denitrator helped

  • Nick…the ASM GS is rated up to 200 gallons so that skimmer should be fine for going plus one.

    The crushed coral “sand” bed…Not a fan of them for a couple of reasons:

    – they trap a lot of detritus (fish poop, uneaten food). SO they can become nitrate farms
    – with crushes coral, you can’t keep certain types of fish like gobies that turn over the sand bed b/c the crushed coral is so coarse.

    Since you have damsels as well, I’d take out the crushed coral and get of those D@mned damsels at the same time.

  • Nick Vento says:

    LOL yeah I want to get those D@MNED damsels outta of there for sure, how do you suggest getting the crushed coral out? I would have to pull out all my rock huh, how should I go about doing that?

  • Best case would be for you to pull all the rock out and then scoop out the crushed coral. Add in the new sand, re-scape your tank and fill the tank back up

    Note: your tank might see a small cycle due to the removal of the crushed coral, but since you don’t have any corals and only 1 fish, it shouldn’t be a problem. I also recommend using SeaChem’s Stability to prevent any cycle in your tank. I use it in every new tank I setup and it works great. I cycled my 90G in 4 days with it.

  • Nick Vento says:

    Cool thanks I did want ot go with sand in the first place I dont know why I changed my mind at the last minute, should I buy the bags of “LIVE” sand or just a bag of dry sand? I heard that those bags of live sand arnt very good to use do to it just sitting on the shelf in the bag somthing about the water being stagnant or somthing like that

  • Nick Vento says:

    Sorry about going off the subject of Nitrates by the way

  • Andrew Larkins says:

    My nitrates was always around 5ppm worst case and if it ever got to 10 then a water change seemed to fix it. Soyes the Octozin dose does seem to correspond to this. Unless the SPS, hammer coral and 1x bubble tip anemome added results in massive Nitrate build up.

    Maybe “bio filter” is wrong terminology. I am referrign to the filter material, bio ball equivalent with Bio lite in the middle of the sump – between the skimmer in 1st compartment and return pump and UV filter in 3rd compartment.

  • Hmm..I’m suspecting the “bio” stuff you have in the middle compartment of your sump. Bio balls were very popular when I first got into saltwater tanks back in the 1980’s. Slowly we discovered they were nitrates factories and really did more harm than good.

    I’d remove the “bio” stuff and put in a refugium. How big is that center compartment?

  • Nick…I’d be more concerned about grain size than “live” or “dry” sand. Don’t go too small on the grain size. I recommend at least a 1mm grain size. This will make the grains big enough that they won’t blow around, but small enough that you can have sand sifting fish like gobies.

    Here is a link to the sand I like and use:

  • Nick Vento says:

    Hey thanks Mark I really appreciate what you do and look foward to seeing some new videos and learning, im going to be switching to sand A.S.A.P., thanks again

  • Nick Vento says:

    Ok so this is what I have in my tank I guess its not crushed coral its Natures ocean
    Premium Aragonite reef substrate 1.7-2.5mm in my main tank, is that size to big? I also have Natures Ocean Bio-Active Live Aragonite natural white #1 in my fuge, how does that sound, too big of size in my main tank?

  • That substrate is pushing it. I’d like to see it smaller – Their Aragonite Sand #1 is a better choice.

  • Nick Vento says:

    Ok thank you for the advice

  • jodi says:

    Do you prefer sand or CC?

  • Sand all the way.

  • Andrew Larkins says:

    Mak – thanks for the advise. As a newbie I am rather concerned as all the shops here are driving us in the direciton I have. What is a refugium and how do I build one? – you have a link or explanation I can go to? Dimensions of the middle compartment I will get later today and revert back.

    That being said I do have a 10cm layer or so at the bottom of the display tank – need to check the average size of the grains ut I would guess at under 2mm per grain.

  • patrick says:

    where do you get the cool t-shirts? … love them!

  • Tell them I sent you!

  • Billy says:

    I love your purple tang… It really stands out in your tank!…i love your setup

  • Murat says:

    Good video, appriciate your help in here. Some say there should be some nitrates to keep softies healthy and thriving and should never be allowed to drop zero levels. Is this true or a myht ?

  • Murat…I see both side of this argument. Softies like dirty water which makes them easier keepers.

    At the same time, I have plenty of zoas in my tank (0 nitrate, 0 phosphate) and they are thriving and reproducing.

    If you wanted to run a softie tank, you could get by with higher nitrate levels. For mixed reef guys like myself, I keep my nitrates at 0

  • Thanks Billy. My purple tang is my favorite fish. I waited a long time to get him and I’ve had him for over a year now

  • Debbie says:

    Hi Mark – I hope this is the right place to comment on nitrates as the video is a quick tip above on vitamin supplement. I saw the nitrate video on You-Tube again as a review. I have just developed a problem with cynabacteria along my sand bed in the front of my tank. I have been doing 5 gal/wk water changes on my 54 gal tank and was suprised to find my nitrates up to 20 and phospate up as well despite a reactor and using ro/di water. I am assuming I feed wisely my fish in what they can eat in 2-3 min and I target feed the few corals I need to. My tank is just about 6 mths old and I am now wondering if using the bio-ball wet-dry system is beginning to be a problem. The bioballs do not look dirty but below their plate there is a fine layer of I guess it is waste – not sure. Looks like brown sand. I did a 10 gal water change last night and put in a phosphate sponge in my reactor and took out the phosban. This morning the nitrate is still high and the phosphates are as well. I have a urchin protein skimmer that is for up to 75 gal tanks which gives me about 1/4 cup or less of skimmate a day. I was hoping I could get your opinion on removing the bio balls and placing live rock in there ( it will not have any light though) I currently have 60 plus lbs of rock in my tank and 2″ plus or so of sand. Its a corner tank so I am limited in space somewhat. I have two power heads and a double return on top so I do believe I am getting enough water movement. I remove the cyno in the am and by the pm it is starting back. Lights are on about 10 hours but that includes moon lights. Thank God I see none of this on my coral or rock but I am concerned never-the- less. Again, would appreciate your thoughts.

  • Debbie…the bio balls will be part of the cyano issue. I’d remove them and the detritus layer underneath them.

    Rock placed in place of the bioballs is a good start, but the rock needs to be submerged

  • logan says:

    Hey mark i have never had my nitrates below 20ppm They are now around 80ppm the tank has been set up for around a year and im wondering how to get them to zero

  • Dave Powers says:

    Hi Mark,
    I was wanting to watch the video you posted about Nitrates but the video attached to this post is about feeding your fish Selcon.

  • Dave…the link in post is for the nitrate show, but here it is again in case there is something strange on your end:

  • Ken says:

    Hey Mark, great post. I have a 200 gallon tank with 3 fish, 2 shrimp, and like 200lbs of live rock and my nitrate levels are at around 50-70ppm. Whats the best way to get rid of the nitrate? Thanks in advance.

  • matthew says:

    i was wondering if i could use any type of plants to lower nitrates

  • Saltwater fish boy says:

    Do you know anything about the ATI bubble master skimmer??????:) I can’t find anything on the internet and was hoping you know anything about it.

  • Vinnie tako says:

    Hello there I want to build a fuge but I don’t know if my sumps arrangement will allow it there is a big space for it in the centre my skimmer is on the left were the drain comes in and far right is the pump the water flows over the top as it outs from the skimmer via a worry is the pump will suck the sand from the gap as its at the bottom..can do I need sand and rock for a fuge

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