Well, by the time I got to this thread you got it all covered, guys, good job!

Still, for my 2 ¢, I will share this story:

I started a guppy tank a few years ago, when I thought of getting garters, because I read that I would need them.
I googled my way to some great fancy guppy sites, and I found this little fish shop in San Francisco, where a guy from Hong Kong told me that he couldn't sell me his expensive guppy fish without me first bringing him a sample of my fish-tank's water.
He wanted to make sure I wasn't going to kill his fish by neglecting the water. Mentioning garters to him was out of the question.

Turns out that in Hong Kong there's quite a cult-following for small fishtanks with six inches or so of light, calcium-heavy, gravel; full of Java Ferns, Java moss, and faster growing water plants. If the tank has the right load of cycle bacteria, and some snails, then, even without filters (I use one), they break down the ammonia and the plants take up the byproducts of that, leaving no food for algae to even grow, while also hyper-oxygenating the tank. The result is a tank that only needs a partial water change once a month, yet it's much healthier and stable water than what one gets from the high-maintainance, high chemical, style of fish-keeping.

The plants also create a darker place, less stressful, with plenty of hides for fry. I was told to keep many females (3 or more) to a male, or I'd lose my female due to the constant harassment from the male. If not breeding you can have two tanks and separate them by gender. Males are not territorial if there are lots of them. Feed only once a day and not a lot. They will snack on some plants. If the sand gets covered with uneaten food and dirt, the system is not working. a slice of cucumber or zucchini will give your fish a good extra snack, it will also attract the snails.

When the snails over-breed, which they will do if they are good mollusks, you can use the cucumber to catch them.

My tank became two tanks thru the years, and now I'm back to just one.
My garters have not used them at all, my scrubs all have eaten fillet right away, so far, fingers crossed!.
I love my guppies now, though, so Im keeping them.
My only addition to the Hong Kong formula: Distilled Water.
We have sulfur in the water here; good for your skin, bad for the tank's bacteria.

Sorry for the very longish post.