Nitrates are out the roof with 90g water change...HELP!


New member
All parameters, including Amonnia, Nitrite, are in the zero to .05 range. My nitrates are at 50mg+. We have done two 45g water changes over the last two days, and after testing, nothing has changed. I have a 180g reef with a 90g sump/ fuge in basement, with 20 fish, only 6 that are over 4". We feed twice a day, and fish are thriving and appear fine. All corals appear fine. Tank has been set up for almost a year using cured live rock, and sand from my 125g. I am just puzzled why I am having Nitrate problems. Checked RO water for Nitrates, and comes back at 0 as well. Any ideas would be appreciated. Thanks!! Marie


New member
Idk if its just me but two 45g changes is a lot in two days and is 1/3 your tank.
When is the last time you did a change? there could be multiple reasons why they are high, starting with the fact that youve taken 1/3 of the biological that was in your water column out..

have you ever heard of Dr.G? Ived used his nitrate remover and it works wonders

and how is your fugr doing? usually plants feed on nitrates, which make your predicament even more complicated


New member
Correct me if i'm wrong but doing a water change should only export built up nutrients, not remove any biological filters. All of that should be living on/in your rocks and substrate.

MBuck: If you've had a nitrate problem for sometime now, it could be possible that your sand/rocks absorb some of the nitrates and could be leaching it back out slowly. Also, you might want to double check your nitrate test kit by testing your RO/DI water. It should come out zero.

Randy Holmes-Farley

Reef Chemist
Premium Member
That's correct, it won't impact the biological filtration capacity.

There are many ways to reduce nitrate and phosphate. I use organic carbon dosing (vinegar) GAC, GFO, skimming, and macroalgae growth.

This has more:

The “How To” Guide to Reef Aquarium Chemistry for Beginners,
Part 4: What Chemicals May Detrimentally Accumulate