do I need a better filter?

[stillwearingaredribbon]

I have a fairly new cold water tank, few months
I am not sure the advice I got has been great, it was from a proper shop and the guy is keen
I bought the tank off a bloke as a 60L but am pretty sure it is 50L going by the dimensions
I did the fishless cycle and the fish shop guy tested the water for me
I put (gradually) 8 minnows and a sucker fish
the sucker fish has died and 1 minnow has died
I have a lot of algae but have started having the light on only for short times
The fish guy told me I could have twice as many fish
The filter he sold me is an aqua flow 50 and you put a whole new bottom part on it every month
I am doing approx 25% water changes every 7-10 days
The water looks clear but the filter seems less effective than when I first got it and wonder if I should have a more effective filter
I don't want to get another sucker as I have since read that they grow big, thats why I have avoided goldfish
Is there anything else I could put in to eat the algae?

[EauLittleRougeofBethlehem]

Nonononono, you cannot have twice as many fish. Stop listening to the shop guy, he may be keen but he's wrong.

I've had a google and the Aqua Flow looks like a fairly basic internal filter- nothing wrong with it, no bells and whistles but it will do the job in a well stocked tank. It may be on the small side for your tank so an upgrade would help.

The bottom part you are replacing every month is activated carbon. It's not completely necessary to use it if the water quality is OK. It's expensive to keep replacing, so a lot of fishkeepers don't bother with it at all and just stick to normal sponges. If you do want to continue using it then replace it every month like you are doing.

You will need to rinse out the other filter sponge with water taken from the tank. Do NOT use tap water to clean the sponges, that will kill off all the good bacteria and your water quality will take a nosedive.

You'll need a water test kit to monitor the water quality. Something like this (shop around, you might find it cheaper) will do what you need.

This explains what you need to know about the nitrogen cycle. How long did your fishless cycle take?

The algae is probably down to the water. If you test then you'll know what's going on. You may need to do a phosphate test as well which the mini test kit doesn't test for, but a good aquatic store should be able to test it for you.

[stillwearingaredribbon]

No worries. I was not planning to add any more
Do you think I am over stocked now?
My filter only has one sponge which gets replaced each time the bottom part is changed. This is why it worries me, I read the sponge is important for keeping the necessary ?bacteria in the tank but all my sponge will be thrown away each month

[stillwearingaredribbon]

Thanks also for your very informative response
I will look at a test kit.

[EauLittleRougeofBethlehem]

Yeah, you shouldn't be replacing the whole sponge, you will be chucking out the good bacteria. Some filters have the activated carbon attached to the regular sponge so you have to throw the whole lot out. If you can't find a plain sponge to fit your filter then you can buy a sheet of pond filter sponge and just cut a piece to the right size.

You could keep the fish you have, you are on the cusp of being a bit crowded but you should be fine if you keep up with the cleaning.