Always Had Trouble Keeping It Clean

[osiris]

The sevs are about 6/7 inches which isnt huge for sevs. I cant just out of the blue buy a 400= litre tank i simply dont have the room or the money for it.

Il start to investigate an external filter... always wanted one but how hard would it be to change from this filter to an external... id have to cycle the new filter while i still have this one running??

 

[ChilliPepper]

Oh, you only have an internal?

I'd suggest an external filter capable of filtering over 6x the turnover of the tank, so you want a filter with a l p/h of at least 1,500. Also waterchanges of at least 30% a week.

When you get the new filter, put as much of the old media from your old filter in it as possible to seed the filter. I'd also consider running the old filter as well (get new media), as you really need as much filtration as possible with your stock in this size tank.

I understand you can't just go out and buy another tank, but your Sevs should get between 10-12", so that along with the other fish makes it an incredibly overstocked tank. At the end of the day, it is your decision as it's your fish, and I can only advise. But if you wonder why you struggle to keep your tank clean and if you have any aggression issues in the future, then the root of the problem is always going to be that the tank is too small for these fish.