Very high nitrate

[TDB]

My tank has been cycling for 3 weeks then tonight I had these readings

Nitrate 160 ppm
Ammonia 0
Nitrite 5.0 ppm

Two days ago the readings was
Nitrate 20 ppm
Ammonia .50 ppm
Nitrite 5.0 ppm

What do I need to do ?

[billdogg]

Retest first, then assuming similar results, a water change. Sounds like you are just about ready for fish!

[TDB]

Originally Posted by billdogg

Retest first, then assuming similar results, a water change. Sounds like you are just about ready for fish!

Yes I did retest after it changed so much. How big of a water change ?

[ReefsandGeeks]

I've read a 50% water change is typical for after a cycle, but that will only get your nitrates down to 80ppm (assuming your nitrates were actualy 160, and not "off the charts". Personaly, I'd do a 75% water change and retest nitrates once the cycle is complete. Then you can add your first fish. The good bacteria lives on surfaces and in rock, not in the water. so you can change alot of water without effecting your biological filter.

[tmz]

I'd wait a few weeks for the nitrification and denitrification cycles to work.

The nitrite(NO2) means nitriifcation is still occurrng ,producing nitrite then nitrate from ammonia .
It also takes time for denitrifying bacteria to become established and to reduce the nitrate via anaerobic activity ,taking the O from NO3 leaving N to combine with N to form N2,nitrogen gas which bubbles out of the water.
If you still have unacceptably high nitrate with 0 ammonia and 0 nitrite after a month or so , a water change can be useful.

[TDB]

Thank for all the advice. Everyone on RC is great !

[Puffyluv]

Actually, changing half the water won't reduce the nitrate by half if you have rock and sand in there....it would take more like 80% for that. This is because most of you nitrate is living in the rock, and the sand.

I would personally drain the whole thing and fill again, and this time not spike it so high. But, that is mostly because I am cheap and wouldn't want to spend so much on many, many, many water changes...

[gone fishin]

FWIW I have read that with nitrite present it can skew a nitrate test. Good luck

[TDB]

I did a 25% water changes yesterday. I tested again this morning and everything was back in line with where they should be.

Ammonia 0
Nitrite .25
Nitrate 40

[dkeller_nc]

Originally Posted by Puffyluv

Actually, changing half the water won't reduce the nitrate by half if you have rock and sand in there....it would take more like 80% for that. This is because most of you nitrate is living in the rock, and the sand.

I would personally drain the whole thing and fill again, and this time not spike it so high. But, that is mostly because I am cheap and wouldn't want to spend so much on many, many, many water changes...

FYI, this isn't correct. Inorganic nitrate is highly soluble in seawater, so there's no reservoir of precipitated nitrate in your rock and sand that will re-dissolve after removing a lot of it with a large water change. But since there's often a lot of organic material in rock and sand, the nitrifying bacteria that are present can make a lot of new nitrate very quickly, so it appears to an aquarist that the water change didn't reduce the nitrate concentrations as much as the water change percentage would indicate.

Overall, water changes really aren't an effective way of dealing with nitrate production long-term. Instead, one would like to remove it with biological processes, as detailed in this article.

[Puffyluv]

Interesting...though that sounds really impossible. Not much about a nitrifying cycle is "quick"...this change occurs in the 15 minutes after changing and before testing?

Also sounds pretty impossible to do a 25 percent water change with 160 nitrates and come out with 40...OP...are you maybe using API, and not shaking bottle 2 enough?

[dkeller_nc]

No, you're correct - appreciable nitrification isn't going to occur in 15 minutes. I was speaking about instances when the aquarist notes a nitrate level of 80ppm or more, performs a 50% water change, and tests within the next day or two and finds 50 or 60 ppm.

[tmz]

You are welcome TDB.

I agree nitrate doesn't "live" in rock and sand ;it's soluble . Stir ups with water changes can realease particlate or dissolved organic organic matter which can pollute a test sample .
To iterate and to be clear , I don't think a water change is needed during cycling unless ammonia levels are very high. The presence of nitrite indicates the nitrification cylce hasn't finished; the tank is not ready for animals due to the liklihood of continued ammonia or a secondary spike. The high NO3 likely indicates the denitrification cycle isn't in gear yet.

[TDB]

Originally Posted by Puffyluv

Interesting...though that sounds really impossible. Not much about a nitrifying cycle is "quick"...this change occurs in the 15 minutes after changing and before testing?

Also sounds pretty impossible to do a 25 percent water change with 160 nitrates and come out with 40...OP...are you maybe using API, and not shaking bottle 2 enough?

I am very sure the water change did not change the nitrates from 160 to 40. I thing it was something else

[Azedenkae]

OP maybe have plenty of nitrate-reducing bacteria?