To filter or not to filter, this is the question

[ParadoxLiz]

If you have a canister filter and you shut it down then you can toxify your water in the filter and when you fire it up you will blow that bad water into your tank.

Jericho,

Is this because the water is sitting and the bad stuff somehow multiplies, or...? I'd be very interested to understand what's going on here and the timeframe so I know how to avoid it without doing more work that needed (a full cleaning on the canister is quite the process, involving overnight soaking in a chlorine solution, and I only use the canister for water changes - suck the bad stuff out of the tank into an empty bucket, suck the good stuff from another bucket with treated and aged water into the tank). Right now, I do the cleaning process after gravel washing or using the canister to clean a murky tank (from recent planting), but not after every water change.

Thanks,

Liz

PS: I have other filters for 24/7 operation - this is just for easier cleaning/water changing.

 

[ghinksmon]

A stagnant filter will have low or no free oxygen as it is used up by the bacteria cultures. Turning on the filter pumps this oxygen poor water into the tank. In addition to the low oxygen you'll create a nitrate spike as the relatively small water volume of the filter has been steeping in your filter debris. A prolonged down time in a canister filter would likely result in conditions of anaerobic decomposition as well (methane, acids etc).

 

[RTR]

Canisters, and other filter types, are strongly aerobic (O2 rich) environments in operation. Even when debris builds up, the filter retains a high O2 level due to the constant replacement of the water. When the filter is off, the millions of bacteria living there consume the available O2 quickly. After that, they die and rot, so in addition to now anaerobic (lackingf O2) debris, you have all the good bacteria dead and contributing to the problem. The time span will depend on the biload house in the filter plus the debris load when the flow stops. This is not something you want to risk.