water change questions

[wla1610]

What is the biggest % of a water change that can be done w/o causing a cycle?
Also, how often can a water change be done w/o causing a cycle?
I'm asking this because my nitrates have managed to get up to around 20 now. I realized I needed to free up my refugium a bit due to the amount of algae that had grown. I really need to get my nitrates down. I'm hoping I can get them back down fast enough before my acroporas die.
Thanks,

 

[phixer]

Not sure exactly what your asking. This is a difficult question to answer without knowing the paramaters of your H20 and what your tank contains. Many causes here. In theory, you could change all of your water and not cause the tank to re-cycle as long as there was sufficient bacteria left to continue the cycle. Dont know why anyone would want to take the chance though. Reduce your feeding, and stick to a constant water change schedule. Reduce the number of inhabitants (if crowded) check for dead tankmates or rotting food.
5% of water weekly is a healthy exchange. It is frequent enough to keep the nitrates down and of a small enough amount to prevent stressing the inhabitants.

 

[murph]

Vary little if any of the bacteria that maintain your bio filtration are in the water column. They exist in and on your rock, filter media sand and even the glass so setting off a cycle with a water change is highly unlikely.
You do have to be careful of other rapidly changing parameters with large water changes however.
Test your tanks water for PH and alk and then test a fresh batch of your change water for the same. If they match large water changes can commence. If not smaller changes are in order for a week or so until they do match and then you can go ahead with larger changes to bring down the nitrates.
Of course match the temp and SG of your change water to that of your tank on every change.

 

[1911_guy]

Originally Posted by Murph
Of course match the temp and SG of your change water to that of your tank on every change.
I have done several large water changes on my 75G and totally didn't even think about matching the 2. I definetly will in the future though, thanks for mentioning this.

 

[merredeth]

When using some medications it is recommended to do a 30% water change.
I have always done 20% water changes and if I need to do another, I do it the following day and go 10% until problems were eradicated.
Denise M.