I had this post in another thread, here's the copypasta:

I made an impulse purchase. I know I told you all I wasn't planning on getting any ocsars any time soon, but I made a liar out of myself. So here's the game plan, I'm only hoping it won't give the new fellow HTH disease or stunt his growth:

The oscar I bought is about 1.5 inches big right now. It seems they will grow at about an inch month until they're about 9in or so. So, in about three months (making him hopefully about 4.5, or let's say 5inches to be safe), could he at least semi-thrive (vs 'just survive' since I know they are hardy fish) in a 15 High? At that point he'd (worst case scenario) be moved to a 40 gallon breeder. And then, before xmas, to a final 75 gallon.

These plans are based on my time estimates. My 40 has 3 goldies that I originally wanted to build a pond for on a home bought before late fall. BUT now I have convinced my mom they're easy to care for (for our southwest region compared to places you have to break ice and such), at least that I could when i visit her (she's scared I'm going to leave her completely, I think) if she's not able to do so. However, after pricng the liner, sand, and those concrete blocks, I figure I could do it for her with my next paycheck (so that is in a month, so let's add two weeks to actually do the work). Henceforth, I could move the oscar in as little as a month and a half, but I want the three month safety limit just in case!

So then it goes, will this oscar, of maybe 5 inches in June, be able to be OK in the 40 at 9 inches around October? I am sure I'll find a house (and setup the 75) WELL before that, just trying to err on the side of caution.

Of course, at this point, the best way to do that would have been to IGNORE THE CUTEY MAKING FACES AT ME and not buy him until I was all ready in my new house, or at least until the 40 was empty to start with.

Oh, the 15 will have the filter it came with (biowheel Marineland thing) (plus WCs every 2-3 days), and the 40 has a Marineland power filter ("up to" 50 gals) plus the older Aqua-Tech 30-60. A sponge filter from my 40 will be added to the 15 just to get that one started; I accept daily WCs until I am sure it is fully cycled.

tldr: I bought an Oscar, he's only 1.5 inches now in a 15 high tank. He was going to be moved within 3 months to a 40 gal, and within the year to a 75 gal. However, found a guy on my local CL with a 75 gal w/ stand for sale, and so while we haven't made the deal yet, i expec this means my oscar can live in the 75 within 5-6 months :D

So I was wondering, while he's young and not huge, are there any good tankmates he can have in the 15 gal? I do not want a second oscar or anything, because I wouldn't have another 75 for that fellow when they get older. Preferably, fish that can either stay in the 15 when he's gone, and/or in the 40 that I will be vacating regardless? Thanks for any advice on this part!

Oh, so far going through a mini-cycle as I used some older filter media on oscar's new tank (he has no name yet, alas), so I don't want to add anything until it settles a bit.