Can I leave my Fluval fx5 running while doing my normal 30% water change as long as my intake is below water line? When I do have to turn it off how long until I risk bio damage?

as long as water runs through the filter you can keep it running

I leave mine running... never had a problem

Same here...leave mine running. Only thing I unplug is the heater if the water will go below the "minimum water line" on the heater.

With canister filters there is normally a minimum distance that the water level should drop down compared to where the canister is located, it should tell you in the instructions, it does in the Eheim instructions. Anyway, it's perfectly okay to leave the canister running as long as the water doesn't get down too far.

As long as the canister is full of water when you turn it off it will be perfectly okay for an hour or so. Bacteria will start dying off as soon as they are deprived of oxygen, but it does take a long time before irreversible damage is caused.

I shut mine off when adding the new non-treated tap water, and restart it after all the water and Prime have been added. I may not hurt your bio filter to leave it running, but it also doesn't hurt to have the filter off for 10 min.
Just my 2 cents

a big pro for canisters compared to sump.
You can leave them on during waterchanges.
If i'm cleaning the tank with the sump, i allways feel the clock ticking when the filter is turned off.

Leave it running, but add the dechlorinator and wait a few minutes before refilling!

delboybully wrote:


you can do it either way. if you leave it running make sure you add the water conditioner before any new water goes into the tank or the untreated water can end up in you filter. turning off for a short time is another option but you must remember to turn it back on. if it was off for 20 mins or so all would be fine. when adding conditioner to the tank you should add enough to cover the tank volume IE if you tank is 100g you change 30g of water you should still add conditioner for 100g. its not the most economical way to change water and I wonder how many of you guys actually do add the full amount of conditioner???

marcus wrote:

Uhm, do you want an honest answer, Marcus.

I just add for the new water volume, but that's gonna change from now i guess.
That'll help to get my tank of condition empty a bit quicker.
So i finally can switch to Seachem Prime.

I only add for what I removed... The rest is already treated!!!

but it will mix with the rest of the water...
I'll check what the container says...
it says 5 mil per 20 Liters of water, it does not say 5 mil per 20 Liters of new water.
So, now...?