Much snippage
Regarding a canister filter going anaerobic in 45 minutes to an hour, this
too sounds like a short time for the results being seen, but it doesn't
sound impossible either. Hopefully more of the bacteria went dormant than
actually died off, so the recovery will be quicker.
--
www.NetMax.tk

It might have been more than that, also it was very hot.
I'm now getting weird test results.
pH on the two larger tanks is down to 6.0, I was getting ammonia on the big
tank (400l) though the ammonia alarm didn't trigger (checked with household
ammonia, it's working) so could be ammonium ?

No nitrite, and Nitrate as low as usual 5 - 10

Peter