Advice Required Please

How long are your lights on for?

Id advise you to reduce this to less than 10 maximum, 8 preferably and preferably less whilst you deal with the algae bloom.

You can do a 'siesta' in the middle of the day also which will help where the lights are off for a few hours during the middle of the day and you have 2 shorter lighting periods.

To double check does the water look green cloudy or white cloudy? Are you vacuuming the substrate?

Ok I think we're on the right lines with reducing the lighting period.

Do you dose any plant fertilisers? Give them a miss this week if you do.

Did you transfer your old filter media into the new filter?

By not transferring the old media you have lost all the beneficial bacteria which treat the fish waste.  You are effectively going through a fish-in cycle.  This is what has led to the algae/bacterial bloom.  Fortunately the large water changes you have been doing have probably been protecting the fish.  Please read here for more information https://forums.thinkfish.co.uk/fishtank-filtration-and-cycling/fish-in-cycling-with-fish-how-to-do-it/.

Afraid I need to log off now but I expect @Sue our cycling expert will be along shortly to advise further. Keep the water changes up in the meantime.

Thanks Matt, I will do as you have suggested. I am also hoping Sue has some words of wisdom too ?

i don't have any of the old media left. I think this is a lesson learnt.

So just to clarify, I need to continue doing small daily water changes, reduce the lighting and make sure the substrate is clean and in a few weeks you think this issue should be resolved ? Because it seems to be getting worse !

Thanks again for your advise

What you need to do now is monitor your ammonia and nitrite levels. Because you have live plants, they will help a lot as plants prefer ammonia over nitrate as fertiliser so they'll take up a lot of the ammonia made by the fish.

As well as following the fish-in sticky in the filtration and cycling section you can also use a calculator to check if the ammonia you detect in a test is in the toxic form or the less toxic form.
https://www.hamzasreef.com/Contents/Calculators/FreeAmmonia.php
Leave the first box as it is, set salinity to zero, then add your readings for ammonia and pH and the tank temperature. Then click calculate. The number you want is in the last box, NH3 concentration.
If this is no higher than 0.02, you don't need to do a water change. If the number is above 0.02, you do need to do one.
But if you see nitrite above zero, any value, you need to do a water change regardless of any ammonia.


It is probable that the bloom is an algae bloom, they are not always green. It started before you changed the filter so that isn't the cause of the bloom, just an added complication. The usual treatment for an algal bloom is a total blackout for 3 days. The tank is wrapped in something thick and left for 3 days - no tank lights, no feeding the fish. The idea is that lack of light will kill the algae. The plants, being bigger, will survive. But you can't do that right now. You need to test the water and do water changes if necessary. And you can't risk shutting the plants down for 3 days as that would mean they take up less ammonia.
I think you'll have to sit out the bloom until you are sure the tank has re-cycled. Once you've had zero ammonia and nitrite for a week, together with cutting down the light time, see what the bloom looks like then. If it is still bad, then maybe think about the blackout.