How to reduce High nitrates?

x4FIR_1 · Mar 7, 2025

So I have a Fluval Evo 13 with a damsel and some corals. I finished the nitrogen cycle a few weeks ago. I did a 100% water change when I got the nitrate spike (around 160ppm), next day added a fish and coral. It's been around 40 ppm or higher since. I've been feeding 1/6th of a brine shrimp cube every other day so just what the damsel eats. I also have been doing a 50% water change every 5 ish days to keep the nitrates down but they still seem to be going up. What can I do and am I doing something wrong?

tbrown · Mar 7, 2025

Why'd you do a 100% water change? 10%-20% is the typical recommendation. Constantly changing large amounts of water can cause some aggressive swings in temperature and pH which can be harmful to fish and inverts.

If your nitrates are raising rapidly then there's an ammonia source. If all you're feeding is a small portion of a cube and nitrates are still rising, you can thaw the portion and rinse the in RODI water. Sometimes the liquid that the feed is frozen in can contain higher nutrients.

x4FIR_1 · Mar 7, 2025

tbrown said:
Why'd you do a 100% water change? 10%-20% is the typical recommendation. Constantly changing large amounts of water can cause some aggressive swings in temperature and pH which can be harmful to fish and inverts.

If your nitrates are raising rapidly then there's an ammonia source. If all you're feeding is a small portion of a cube and nitrates are still rising, you can thaw the portion and rinse the in RODI water. Sometimes the liquid that the feed is frozen in can contain higher nutrients.

I did a 100% water change because I wanted to clear anything left over from the cycle before adding live stuff. I can tone the 50% water change to a 20% but I do heat my water while its mixing. I will try thawing the food thank you.

Mr. Mojo Rising · Mar 7, 2025

What test are you using? What type of filtration do you have? Do you have any clean up crew? Using tap or rodi water? Can we see a tank pic?

Its definitely not the food, its impossible IMO.

And on another note I would encourage you to feed more and better variety. Brine shrimp is mostly water, it has zero nutrition, the fish will eventually starve to death. Feed pellets or reef frenzy once or twice a day.

x4FIR_1 · Mar 7, 2025

Mr. Mojo Rising said:
What test are you using? What type of filtration do you have? Do you have any clean up crew? Using tap or rodi water? Can we see a tank pic?

Its definitely not the food, its impossible IMO.

And on another note I would encourage you to feed more and better variety. Brine shrimp is mostly water, it has zero nutrition, the fish will eventually starve to death. Feed pellets or reef frenzy once or twice a day.

Api reef test kit, as of now just some filter floss and a piece of dark rock from an established tank, no clean up crew yet, using my own 0 tds rodi water with instant ocean salt. Sorry for the low quality picture.

tbrown · Mar 7, 2025

You're going to get a lot of flack for using API but they're decent enough to give you a ballpark.

Just curious, have you ever tested the IO after you've mixed it? I have heard people in the past having similar issues and they tested the mixed salt and it had nitrates showing up so the water changes were actually increasing nitrates.

x4FIR_1 · Mar 7, 2025

tbrown said:
You're going to get a lot of flack for using API but they're decent enough to give you a ballpark.

Just curious, have you ever tested the IO after you've mixed it? I have heard people in the past having similar issues and they tested the mixed salt and it had nitrates showing up so the water changes were actually increasing nitrates.

I did not think of this I will do this next water change thank you.

tbrown · Mar 7, 2025

x4FIR_1 said:
I did not think of this I will do this next water change thank you.

Especially doing larger water changes, you will see more of an impact.

Fish Fan · Mar 7, 2025

tbrown said:
You're going to get a lot of flack for using API but they're decent enough to give you a ballpark.

I'll agree. There's a lot of hate for the API test kits, but they are not horrible, and widely accessable. Use them to identify trends, and not so much as a precision laboratory instrument.

Good luck!

Mr. Mojo Rising · Mar 7, 2025

x4FIR_1 said:
Api reef test kit, as of now just some filter floss and a piece of dark rock from an established tank, no clean up crew yet, using my own 0 tds rodi water with instant ocean salt. Sorry for the low quality picture.

Ok, so its not a great test kit, salifert is better.

Filter floss actually holds food until you change it out, which means nitrates will increase while the food rots, so you should change that out every few days.

Your filtration system includes no nutrient export. Example of nutrient export is protein skimmer, water changes, refugium, and carbon dosing. These methods export nitrate out of your system. Aquarium keeping is all about nutrients in vs nutrients out. So your water changes are your one and only export method, you should be changing water much more frequently than every 2 weeks.

Nutrients should not be controlled by food, by feeding more or less, thats not fair to the fish. Nutrients are controlled by filtration. Get some clean up crew to eat up uneaten food.

And lastly I'm sorry of it sounds like preaching, not meaning to. Good luck

tbrown · Mar 7, 2025

Mr. Mojo Rising said:
Ok, so its not a great test kit, salifert is better.

Filter floss actually holds food until you change it out, which means nitrates will increase while the food rots, so you should change that out every few days.

Your filtration system includes no nutrient export. Example of nutrient export is protein skimmer, water changes, refugium, and carbon dosing. These methods export nitrate out of your system. Aquarium keeping is all about nutrients in vs nutrients out. So your water changes are your one and only export method, you should be changing water much more frequently than every 2 weeks.

Nutrients should not be controlled by food, by feeding more or less, thats not fair to the fish. Nutrients are controlled by filtration. Get some clean up crew to eat up uneaten food.

And lastly I'm sorry of it sounds like preaching, not meaning to. Good luck

He said he's doing 50% every 5 days.