I have been noticing the bigger my oscars get the harder is has been for my biologicals to keep nitrates down so I bought some of the bio-max to put in my filter. They look like ceramic straws with a rough exterior that are suppose to work great. On my HOB filters I took the carbon from the cartridge and placed the bio-max inside which has greatly reduced nitrates but today I ordered another cannister just to make sure that my water quality will be the best possible. It has 4 baskets so what are the best materials to place inside for optimal filtration? Also, I plan on switching from gravel to sand this weekend because I really like the way it looks. Will this mess up my filters? Thanks - Jon

Give us some indication of how quickly the nitrate levels are raising, for instance on the fourth day after a water change, what are they?

Remember the more water you've got, the slower the nitrate levels will rise. Maybe you should consider getting a bigger tank at some stage?

As for the canister filter, I would fill all trays with biological filtration, leave a little bit of space for some mechanical filtration, maybe one or 2 inch thick sponge. Even though mechanical filtration is a good idea, especially with messy fish, biological filtration is what will cleanse your water of toxins. For this reason, get as much biological filtration into the filter is possible. Remember you can always gravel vac to remove the waste that has left behind.

I would do as OFL say, use a small amount of sponge and fill the rest with bio filtration. It can be the hollow tubes or the little rocks that look like small sponges or any other sort, it doesnt matter as long as it has a large surface area as this is where the bacteria live

Well, I forgot to mention I had to take one of my baby oscars and put it with the larger one because he is growing so quickly. He is getting reloacted but I still want him to be happy/healthy. I gravel vac with water change 2x a week as is I just noticed it going up a little quicker.