I'm thinking about adding another filter to my system. I already have two filters on my 90 gallon a Penguin 350 Bio wheel and a magnum 350 canister.
They keep my water parameters in check ,but I don't think you can have to much filtration with Oscars. Unless they can't swim against water flow and it keeps them pasted against the glass. What do you all think. Can you have to much filtration.

In the uk bio wheels are not very popular. most go with canisters or sumps. the mag has 350gph I think thats right? and my guess is the wheel has the same. so you do have enough with just the 1 magnum the wheel gives a backup so you could get away fine with what you have. I have always liked the idea of 2 instead of 1 large filter just in case one goes wrong.

They always say you can't have too much filtration. However this is partially untrue. This is my way of thinking. Let's say you have a 55 gallon tank with one adult Oscar. On that tank you put a large sump filter with enough biological filtration for 2000 gallons. You wouldn't be able to then take that sump filter and put it onto a much larger aquarium with lots more fish and expect it to cope with the increased bioload. In other words the more fish you have, the more bacteria we will need to cope with their bioload. Piling lots of filters onto your tank isn't going to give you a huge benefit. Using twice the filtration is more than enough for what you need.

My sump filter is something like 40 gallons, at the moment I have enough biological media for something like 3 1/2 thousand gallons. That doesn't mean I could take that sump filter and put it on a 3000 gallon pond packed with fish and expect it to do the job properly.

Yea the two filters do just fine on my tank. But I have an idle Hot Magnum that I'm not using at the moment. I was thinking about adding it to the system.
I think it would be better than the Penguin HOB. Besides I could get the bacteria
started in it. Just in case I want to set up that empty 65 gallon I have.
"O" No! you see where this is going; Damned MTS.

I think it would definitely get it started by putting it on an established aquarium that already has bacteria present. I think it would still take a little but of time before that filter was ready for another tank

Yea I was thinking the same thing. Do you think the Hot Magnum would do a better job than the Penguin HOB when it is established? The Hot magnum doesn't have the output of the HOB but will have more Media.