Debating a new (first) 20-gallon tank after too much 10-gallon angst

[alivenwell82]

Over the last 10 years I've had a series of minimally to moderately successful 10-gallon tanks, all of which I ultimately give up on because maintaining the water quality becomes such a pain in the neck.

No matter how many partial water changes I do, no matter how often I test and no matter how low a bio-load I try to maintain, the levels and temperature seem to rise and fall too much, too fast and ultimately the water quality deteriorates faster than I (or I think anyone with a full-time job) can keep up.

This especially becomes a problem in the summer when temperatures rise. I don't have air conditioning.

Thus the empty 10-gallon tank in the corner of my apartment.

But, I'm debating whether to start a 20-gallon or 25-gallon tank in hopes that the increased water volume will mean more stability and less gray hair.

I'm looking for suggestions on how to outfit it. A local store sells a 20-gallon high that comes with a Penguin 200. But since I already have a Penguin 100 (in theory good enough for up to 20 gallons) I wonder if I should just buy a second 100 and run them both. It would seem the added benefit would be that if one fails for some reason, you at least still have some filtration

Also, the set-up comes with a submersible 100-watt heater.

Lastly, I still have some of the gravel from old tank, but that hasn't had any fish in it for more than a year. Would it help jump-start my cycle to use that, or has it been too long? I would think it's been too long, but, then again, what do I know?

I appreciate any advice. Thanks!