# High nitrate problem



## ladybev (Jun 10, 2008)

We have a 100gal. tank, 6 months in operation, with 2 4in. oscars.
We have done 3 25% waterchanges on 3 sucsessive days, and still have nitrates at 40ppm. 
What could the cause be?
Thanks


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## DJRansome (Oct 29, 2005)

Do you have Nitrates in your tap water?

What were the Nitrates before the water changes?


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## Toby_H (Apr 15, 2005)

DJRansome said:


> Do you have Nitrates in your tap water?
> 
> What were the Nitrates before the water changes?


^^Important questions...

Is there a dead fish, fish poo, dead plants or other organic waste that could be in the tank breaking down? These things are continually adding to the pollutants in your water...


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## alicem (Jul 26, 2007)

Sorry, more questions:
Do you move the decorations (ie rocks, driftwood, etc) and vac the gravel weekly?
Do you feed small amounts, so that the food gets eaten _before_ it lands on the substrate?


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## ladybev (Jun 10, 2008)

Thanks for your quick responses.

We are using RO DI water exclusively.
Given oscars usual dislike for them, there are no live plants in the tank.
Only 2 fish to keep track of, so no one is unaccounted for.
We vacuum half the gravel one week, other half next week, getting under the decorations.
We feed only what the fish will eat, except for what sometimes gets spit out.

Is it possible that the RO unit is not removing nitrates from water?
When we change 25% of the water, should the nitrate level not drop by 25%?

Thanks again.


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## prov356 (Sep 20, 2006)

> When we change 25% of the water, should the nitrate level not drop by 25%?


Yes, but that may be tough to discern on the test kit color chart.

What type of filter(s) are you running and what's the cleaning schedule?

I'd vacuum all the gravel at once weekly.

I'd also bump up the amount of water changed to about 40%.



> Is it possible that the RO unit is not removing nitrates from water?


Yes. Easy enough to test that.


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## FLGirl1977 (Jul 24, 2007)

I've had this problem once before. The only thing that seemed to help was when we started doing weekly water changes with 50% of the water. You could do one massive water change of 75-80% and then just do weekly of 50%. That will DEFINITELY get your nitrates down. HTH...

-Renee'


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## Joea (May 25, 2004)

RO water should have no nitrates. Overfeeding is a common cause of higher than normal nitrates. 40ppm isn't horrible but it could be a bit lower. Remember that nitrates will never be zero. I would try feeding a little less, perform a large 75% water change and regular, weekly changes of 30% or so and see if they come down.


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## ladybev (Jun 10, 2008)

Thanks again for your responses.

We will try with the big water change and try to get it under control that way.

:fish: :fish:

Our fish thank you all.


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## Barbie (Feb 13, 2003)

Why would you use pure RO water? Nitrates are an indicator of waste levels in the tank. Cut back what you're feeding and you'll have better luck getting them to drop. While they may eat it all, it doesn't mean it's good to feed that much. What they eat in a minute is more than enough, especially if you're having high nitrate issues. Larger volume changes, more frequent changes as previously recommmended are definitely in order. Don't just vacuum half the tank a week. Doing it all will just reduce the amount of debris decaying and polluting the water.

What is your tank TDS? kH? Do you understand how buffering capacity and pH work? If not, you might want to get in and clarify that. The idea of Oscars (high waste making fish) in water with buffering capacity and nitrates that high doesn't bode very well if you really are using only RO.

Barbie


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## prov356 (Sep 20, 2006)

Good observations, Barbie. I assumed, maybe wrongly, that the OP meant they were using RO just for 
water changes in an attempt to bring the nitrates down. But, if they get overly aggressive with that, one 
problem could be solved while another was created.

More info would be helpful like current GH, KH, pH of tank water and if you're buffering the RO before 
using it for water changes.

Are you using RO because you have nitrates or something else in the tap?



> Is it possible that the RO unit is not removing nitrates from water?
> 
> Yes. Easy enough to test that.


i also should have elaborated on this more. If an RO unit isn't functioning properly, or hasn't been 
maintained properly, it may not be removing nitrates or anything else for that matter.


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## ladybev (Jun 10, 2008)

Thanks Barbie and prov356,

We have some ammonia and nitrates (fairly low amounts) in the tap water, which is why we started using RO in the first place.
We understand that RO has a lower buffering capacity, but how could this contribute to a higher nitrate level?
Would you suggest mixing RO with regular tap water, and if so, in what ratios?

Thank you.


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## Barbie (Feb 13, 2003)

Sorry, I was at a convention all weekend so my last post had a few things that I'd have loved to edit .

RO water has no ability to hold your pH. That means that your fish are living in liquid acid at this point. It's really important for you to test your pH and kH at this point. The nitrates are strictly caused by your overfeeding and not frequent enough water changes.

The bottom line is that fish waste is acidic. If you aren't diluting it often enough with water with some buffering capacity, you're risking a big pH crash that your fish won't appreciate. Tap water having traces of nitrate and ammonia isn't the end of the world if you use a product that detoxifies ammonia. Figuring out what your kH and gH are, not to mention the pH of both your tap water and your tank water would be a good place to start, at this point . Diluting it more with RO water shouldn't hurt anything, but you can then add some coral to the filter to slowly bring the pH up again, depending.

Barbie


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## ladybev (Jun 10, 2008)

Barbie,

Thanks for the information you provided.
We didn't think that the lowered buffering ability of RO would cause a change in pH if frequent water changes were done.
I will check the pH, as the last thing I want is fluctuating pH.
Poor fish, we were trying to treat them really well, and ended up possibly making their water toxic.
I will also check kH and gH to see just what the buffering capacity of our tap water is.

Thanks again, you have given me some homework to do.


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## prov356 (Sep 20, 2006)

KH or buffering capacity is the important one. That's the one related to pH, not GH. If buffers (KH) drop 
to 0, your pH will crash (quick and drastic drop). Buffers get used up by acids, and as Barbie said, fish 
waste is acidic. Fish like oscars that produce a lot of fish waste may use up those buffers quickly. You 
should test the tank and keep a log for a while.. Test pH and KH and nitrates both before and after water 
changes. That log will tell you the feeding and water change routine that'll work for your tank, since all 
tanks all a little different. Ideally, I don't like to let buffers go below 5 and like to keep nitrates at 20 or 
below. As long as your pH isn't extreme one way or another, it should be ok.

Using RO water for water changes is fine as long as you add buffers. I think there's a product out there 
that's made for re-conditioning RO water. Mixing it with tap is ok too. But, I think I'd go with Barbie's 
suggestion and just detox. It's a lot easier. Particularly if ammonia and nitrate levels are low.

What exactly do they test out to?

There's some good info here in the forum library. Look at 'Practical Water Chemistry'.


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