First Water Change....How Much??

mpjmeyer · Feb 18, 2017

Ammonia just hit 0 and Nitrites are lowering. Tank is 65 gallons with 10 gallon refugium and sump. When I do my first water change, how much should I do? I've heard people say 20%, 50% and 100%...which is most accurate?

Tank cycling with 65lbs. Fiji dry live rock from BRS along with live sand. No other additives cycled the tank.

Rubicon_12 · Feb 18, 2017

I usually do a 20% WC after the tank has finished cycling, some people do more, some less. I'm sure some of the experts will chime in, but you can't go wrong with 10-20%.

mtraylor · Feb 18, 2017

20% sounds like a good number. Now that you have some beneficial bacteria...you will not want to deplete it with a huge water change.

Cment · Feb 18, 2017

mpjmeyer said:
Ammonia just hit 0 and Nitrites are lowering. Tank is 65 gallons with 10 gallon refugium and sump. When I do my first water change, how much should I do? I've heard people say 20%, 50% and 100%...which is most accurate?

Tank cycling with 65lbs. Fiji dry live rock from BRS along with live sand. No other additives cycled the tank.

Wait till nitrites are zero and you are reading nitrates. Once this happens its best to add 2ppm of ammonia into the tank and make sure it can convert it to 0ppm 24hrs later. Once the tank can do that you should be good to go. The water change at the end of a cycle is to reduce nitrate levels. If nitrates are reading 10 and you want to reduce to 5 do a 50% water change. If you want 0 nitrates do 100% and so on. Yes there is some bacteria in the water but all most all of it is on your rock surface so no need to worry and think you're doing something counterproductive...

mcarroll · Feb 18, 2017

As long as levels all test well (zeros are not a requirement – you do want some algae to grow), I wouldn't bother with a ceremonial water change....just get on with it.

If you have some detectable nitrates, you might wait until those start to decline from denitrification before you start ramping up the nutrients from livestock.

Don't bother adding the CUC until you have algae growth, and even then take it slow.....the usual "fuzz" you see folks grow impatient with in new tanks will only feed a CUC for a day or two in most cases.