I'm going to cast my vote for big water changes also, IF they are done regularly. Big water changes should have no effect on water chem if they are done weekly. Not enough time passes for the water chemistry in the tank to shift away from what your tap water is. Of course if you are altering your chemistry in some way then this does not hold true, but for most casual hobbiests trying to change the ph of your tank is folly anyway.
On your photos at the top, the ones of your 15" managuense. Will my fish look like that? That's the look that I hope to get out of this fish. Can you tell us more about this particular fish?
What do you mean by "unpaired fins"? Which gender will have that physical characteristic? Thanks.
I kept checking the newspaper, and I kept asking the guy at the pet shop about sales on the tank. I got a 125 gallon all-glass tank for $75.00 used. It is an older tank, but it is in great condition. Just wait as long as you can and bargain shop before you spend large amounts of money.