filter question!

[artgecko]

i usually wouldn't recommend sharks... Most are spazzes and way too skittish (and some, like balas, get absolutely huge). If you start them in the 10gl, do them each 1 at a time and do a real quarantine setup (minimal furnishings, etc.) I would provide the pleco with drfitwood and rocks to hide under. Be ready to move them into the 75 asap. The shark will need more swimming room than the 10gl provides (even as a tiny fish) and I wouldn't keep him in the tank more than 1 month at most. Probably similar with an oscar (it will outgrow it very fast). All of these, including plecos, will produce a lot of waste, so I would go with 20x gph for the filters.

For the size tank you are talking about (75gl) 1 each of an oscar, shark, and common pleco will be just about the max fishload... You will need good rockwork and wood for the pleco to hide in and to break up sight lines (but still keep open swimming space for the shark.) I don't want to be a downer, but I can see an adult oscar harassing a shark non-stop. Sharks are predators too, but not territorial per-say and an adult oscar will consider the entire 75 gallon his "turf".

Have you considered any of the slightly smaller less agressive cichlids? firemouths are great and you could easily have a pair or a single one with a whole school of something like giant danios, rosey barbs, or turquoise rainbows. Good alternatives to common plecos are bristlenoses...maxing out at 7", but still very hardy and tough little algae eaters. Severums are also good cichlids to check out. Voracious plant eaters, and great looking adults (maxing out at about 10"). they are less agressive than firemouths even, but still have loads of personality and would make a great "show fish".

here's a cichlid forum that I've heard good things about. I'd post there and ask for feedback on your tank specs and inhabitants. I've never kept oscars, but I know people have issues finding compatible tank mates and the people here might be able to help.

I don't know of any videos for the foam, but it's pretty straight forward, it comes in rectangular blocks, just get a block that is large enough for your filter cavity and trim with a serrated kitchen knife if needed. I cut mine so that they fit snugly, forcing the water to go through the sponge.

Some filter cartridges (I believe marineland and others) have a plastic cartridge with blue mesh batting on one side. Usually these have carbon inside them (you can hear it if you shake). I cut a slit straight down the middle of the blue batting and dump the charcoal out.

Good luck!