im getting a new tank...some questions

[ultramagnus]

i have a 5 gallon tank and im getting a 20 gallon tank
i have the regular filter with a heater and add water conditioner, and waste control twice a month when i do 25% water changes.

is this wrong? I mean my fish are not dying but i want my new tank to be nice. Is their something really important that i should be doing?
Also how do you guys feel about under gravel filters? how exactly do they work and how often do i have to change the filter? are they even necessary? I mean i want to avoid stuff from making the bottom dirty?

any suggestions would be helpful and
thank you

[emc7]

Undergravel filters use gravel as a surface for biological filtration. They are kind of out of fashioin now, but I think if you have gravel anyway, why not get some use from it. They water is pulled through the gravel by a power head or by airstones. You don't change it, you gravel wash with a fat tube on a siphon during water changes or with a canister fillter. Whenever you break the tank totally down, you remove the filter and siphon underneath. For a 20 you only need one powerhead and they are very quiet. If you have gravel, but not a UG filter, you still need to gravel wash. You really only need one filter, but I like to have two as insurance. If your hang on tank filter fails or clogs and you don't notice right away, the undergravel filter will keep your fish alive. The bottom will actually look less dirty with an undergravel filter because the fish poop will be sucked out of sight.