I found it's much eaiser to clean the oscar tank *not* using any kind of gravel or sand. Let's face it--they are poo factories. I sincerely believe even ONE oscar the poo load is enormous.
I use a large bore tubing to suction the water out--the size of a garden hose. You can get plastic tubing like that any hardware store. Then I got a funnel--and there are types with varying degrees and I but the actual large round part, I cut it quite flat (even all sides) so it sucks out lots of poo quickly (since there is no sand or gravel--no worries about sucking those things up!)
To secure it REAL good use aquarium sealent to totally seal up the funnel with the tubing. AWESOME sweeper! But it sucks out a LOT of water in a short time.
Well, sand/gravel DOES store bacteria but since the oscar poos so much, I compensate by using several corner filters. I weigh it down with a few large river stones (boiled and sterilized prior to using). Put the rest with filter floss and never change it. It will turn BLACK in a VERY SHORT TIME!! These ferment bacteria like crazy! Sometimes you will have to clean off the tubing but maybe once every six months you may wish to replace just HALF of the filter floss. Generally you don't need to do this--but the tubing does need occasional cleaning from the sooty bacteria.
Further since these are full of bacteria, if you should ever have to terminally clean your tank, it will start recycling like really quick. Because you have these wonderful pumps full of bacteria.
You can use them with canister or huge over the tank filters, but nothing can be simplier for bacteria banks than these simple cool old fashsioned corner filters!
I love them! With a 55 gallon tank you may just need one, but with 125 gallons you need about 2 or 3 of them--get them for large aquariusm (REMEMBER THESE ARE JUST A SUPPLEMENT FOR YOUR MAIN FILTERING SERVICES such as cannister or over the top filter).
With sufficient quantities of bacteria you won't need charcoal.
