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Bacterial bloom after water changes.


25 Feb 2017
For the last couple of months, every time I do a weekly 50% water change in my Harlequin and Shrimp tank I get what looks like a bacterial bloom. This only last for roughly 24 hours and then clears up again. This tank is one of the earlier Juwel 100 litre tanks with their usual internal filter and I change the fine white filter at the same time. It only seems to happen on this tank, other tanks with double sponge filters and the Aquael Mini Pat powerhead never do this.

The same also happens in the same tank when I trim the roots of the floating plants and top up with less than one litre of water.

Any help or advice would be greatly appreciated.


22 Nov 2015
used to happen to me all the time. I figured it could have been some type of precipitation occurring as I was using fertilisers at the time.
My worst thought was that by uprooting, trimming and moving plants in conjunction with a large water change I was somehow disrupting my microbial populations. Had regular fish deaths around that time too until I switched to rain water and stopped messing with plants/dosing heavily.

Obviously people do all of those things on a regular basis and have no problem but this wasn’t the case in my experience and there could be many reasons for that.

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