How do I lower nitrates?
 

My API kit shows my ammonia to be .25 or less, nitrites 0 and my nitrates to be 40-80 ppm. I'd like to get those nitrates down, but my tap water starts at 20-40 ppm (really hard to tell with the API colors). I did a water change today and added about 3 gallons of RO water, but that's all I had access to. We have an RO tap at our sink, but the tank only holds about 3 gallons. I retested the water several hours later and it didn't seem to make much difference in my 36 gallon tank.

The tank is well planted. I don't understand why my nitrates are reading this high, other than my tap water isn't helping.

What can I do to lower them?

maybe try a 50% water change, but as far as i know, up to 40 nitrates is harmless to fish

There is a common misconception out there that fish can tolerate high levels of nitrates - some swear that up to 200ppm is just fine. Nonsense. I'm convinced that any level of nitrates, especially above 20ppm negatively affect fish health over time. It stunts growth, reduces life spans and makes fish more susceptible to diseases and general health problems.

In natural fresh water, nitrates are too low to be effectively measured.

I should explain that I have 60-80ppm nitrates in my well water (resulting from a 95 acre farmers field across the road) so I have carefully researched and addressed for my situation.

In your well planted tank that is properly maintained, tank generated nitrates should be very low. This is because the plants will process the ammonia before it is converted to nitrites and nitrates which is very good. In spite of popular believe, plants, like water changes, are very slow at reducing nitrates.
And, your water source is a problem.
Here's what I've done.

- Although I don't have a planted tank, I did add several bunches of Anicharis floating plants.

- I built a DIY bio-denitrate filter (documented in the DIY section) but it has not developed the anaerobic bacteria to process/convert nitrates into nitrogen gas. It uses Seachem Matrix and De*Nitrate bio-media.

- I purchased and use an API Tap Water Filter to make deionized (DI) water.
The DI water is treated with Seachem Replenish (minerals) and Seachem's Neutral Regulator and Alkaline Regulator (for pH)

- I use Fluval Lab Series Nitrate Remover (FNR) in a filter with a spare 10g tank in the garage to filter my well water.
I mix this FNR filtered water 50/50 with the treated DI water to produce a 10g weekly water change for my 60g tank. This water for water changes is also treated with Seachem Fresh Trace to ensure sufficient trace elements in the water that fish require.

- I use API Nitra-Zorb in the tank filter to help keep nitrates at bay (about 5ppm).
Note: FNR and Nitra-Zorb are synthetic resins that adsorb nitrates and are regenerated for reuse many times using non iodized salt water.

- I use Seachem Purigen to adsorb dissolved organic solids before they can be decomposed to create ammonia, nitrites and nitrates.

- Because of reduced volumes for water changes, I use activated carbon in the filter to better purify the water.

Why so much trouble? Store bought bottled water is about $1 a gallon and since I live in the country, I have to drive 20 miles round trip to haul it. My mix of DI and filtered well water is about $.25 a gallon.

Before I realized the high nitrates in my water, I lost a lot of young fish. I've been doing the above for over 6 months and have not lost any more fish.

I hope this has some value to you and others that may face high nitrates in their source water.
For others, with nitrate free tap water, I recommend a well planted, well maintained tank that sees a 25-50% weekly water change w/conditioned water to keep nitrate levels as low as possible.

How are your plants growing? What percentage of the tank is occupied by plants? I would say getting a few bunches of fast-growing stem plants, and you photoperiod should be 10 hours/day. Do you fertilize? Planted Water Sprite is a real fast-grower. I have three in my 10 gallon tank.

More fast-growing plants will help reduce the nitrates persomewhat. Plants outcompete nitrifying bactera for ammonia Aside from that, cleaning your filter regularly and trying to keep a clean tank will help some - vacuum 1/2 the substrate when you do a water change. Reducing the number of fish will reduce production of ammonia that can add to nitates.

Steven

My plants are growing well. I can't really guess what percentage - 75% maybe? I have swords, cabomba, crypts, water lettuce, anacharis, all kinds of stuff. I leave the light on 10 hours a day, every day. I fertilze with both Flourish and tabs in the substrate.


I don't feel like I have room for many more plants, other than floating (and those are growing pretty well). I know how plants work, mine just don't seem to be keeping up. I do water changes at least once a week, lately 2-3 times a week because I've been trying to get the nitrates down. Today I did about a 15% change with RO water, so I'm hoping that will help. I don't vacuum my substrate as it's sand, but I do get excess food out. I have 10 cories in there and a handful of shrimp. I'm not going to get rid of any of them. In fact, I plan to add fish, which is why I need to get the nitrates down.

Thanks for the responses. I guess this is one of those things that's just going to take time.

How much water do you change each week? I'd aim for 50% weekly.

You'll probably never go below what is present in your tap water. Mixing RO will help, since it is zero, but you also should be careful that you don't soften the water to the point it's lower than the plants need (4 dGH minimum). Planted tanks with 0 nitrate in the tap can run with less than 5 ppm nitrates, but most people I've talked to still get at least some kind of a nitrate reading on the test. This is why I say I don't think you'll go below what is in your tap water. Possibly going high tech could, because it promotes much faster plant growth, but that's an expensive solution and comes at the expensive of bright lighting (= stress for forest fish).

How long does it take the RO system to fill the 3 gallons? You could maybe fill a bin or a couple 5 gallon buckets with it throughout the week to get more nitrate free water. But I would add something like Seachem Equalibrium to put some minerals back in if you went exclusivly RO water for changes.

I'm okay with not going to 0 - I don't really expect that. I just really want to make sure it's not up near 80, which is were it seems like it is now.

Last night I filled my small bucket (2.5 gallons) with RO, then dumped that into my 5 gallon and refilled it, which is how I was able to do a 15% change this morning. I don't plan on doing RO exclusively, I've just been doing it since yesterday in hopes of getting these nitrates down. Good to know about the Equalibrium. Eventually I'll probably do a mix of both RO and tap to help balance the nitrates in the tap water.

Thanks for the help.

Depending on your source water GH, you may not need to use Equalibirum if you mix tap and RO. A 50/50 mixture reduces the GH by half. So if your source water is 12 dGH, the mixture would be 6 dGH which is plenty for the plants.

But if your source water is 4 dGH, the mixture would be 2 dGH which is a bit low, some plants may start to show calcium and/or magnesium deficiency.

I have no clue what my dGH is and haven't been successful in finding out from the water company's website either. Won't adding Flourish help with deficiencies or doesn't that cover such things?

Adding that RO water definitely helped. I just retested and nitrates are down in the 20-40 range. Or at least they're orange instead of red. Feel better about that.