Water changes during cycling

[Bettafanatic]

Just out of curiosity, when during a fishless cycle would you do a water change? I know it's whenever ammonia gets too high and when you finish the cycle and want to bring nitrates down. But when else?

[KaylNeko]

Pretty much, that's it--if you overdose ammonia, to ensure you don't kill your bacteria, and at the very end. Some people will change about halfway through the nitrite phase too in order to restore buffers, but that's not strictly necessary unless the cycle goes for a long time (like, six weeks plus, same water the entire time).

[jlk]

Ph needs to be monitored during a fishless cycle. Your bb utilize the buffers in your water in order to complete the nitrification process. Without these buffers, nitrification does not happen. As these buffers get used up, your ph can start to fall (and eventually crash) without a water change to restore the buffers. If a crash is left unchecked, the nitrification process will start to slow @6.5ph and completely stop at 6.0ph.

Its debatable whether or not water changes are necessary for high nitrite levels during a fishless cycle. Its been my experience that excessively high levels of nitrites appear to slow or stall a cycle. As the APi test range only detects levels up to 5ppm and a readily available test for high range nitrites does not exist for the general public, at what level nitrites start to cause an issue is an unknown factor. So, some water changes to bring nitrite levels down to a readable level helps to keep a cycle moving forward as well as to re-establish buffers that are critical to the nitrification process. Hope this answers your question!

[Bettafanatic]

Thanks! That's good to know.