Maintenance time...

I have this week off and have decided to catch up on fish maintenance.

I have 3 fish around 6inches, 3 foot tank and a Fluval 3 plus filter.
No gravel, no plants and a large floating spongeball (which I hope
helps to harbour friendly bacterior).
I have a constant battle to keep the water presentable, though the fish
are healthy and lively.

The fish have been offered a home in a covered pond which forms part of
the amenities at my wifes workplace, in which case I would start again
with small fish.

I want to introduce plants again, these are supplied with a small
weight attached, do I need to put them in a container etc.
also is there a link to the ideal setup.
Any suggestions most welcome.
Rog