What is a roach? I've read on this sight of people putting something called roach in their ponds, and was wondering what it was.

Also, I am confused.........One sight says koi need 1,000 gal per fish, another says 100 gal per fish, which would be more correct?

1000 gallon per fish is correct, they can grow 2-4 feet and r fast swimmers compared to fancy goldfish

Well, that depends now, really. Experienced pond keepers, those who want gigantic koi in their oversized ponds, and can afford a 1000$ filter, and those who buy high quality koi for 1000s of $$ worth, yes, they give their fish that amount of water. However, most of us can't afford that, and it itsn't all that neccessary. There is also the issue of how much food is being fed, how much water changes or pond maintenance one can do timewise, and how much plant material is in the pond. There isn't one perfectly right answer to that question, since it depends on quite a few factors. The less time you have for your pond in general, the better it would be if the fish would have more water available, since it takes more time for a larger body of water to be poluted.
If you ask around during shows or pond tours in your local koi club, most people will say somewhere between 200 gl and 500/600 gl. It also depends on the sex of the fish, since females by nature become heavier bodied and rounder, while a male koi stays rather slim. The more body mass a fish has, the more water it needs.

I ALWAYS recommend 1000 gallons per fish, but as a BARE MINIMUM, I'd go with 300 gallons for younger fish and 500 gallons for older fish -- that's PER FISH, mind you. Koi get HUGE and people don't realize that that small goldfish-sized, ten dollar fish has the capacity to grow to three feet and amass a weight of 30 pounds or more, and produce as much waste as a human on an average day.

Gallonage is important, but more important is the filtration -- and that's where the big money lies. A koi keeper can get away with a 2000 gallon, four foot deep pond with minimal filtration only for so long. Sooner or later the fish will catch up and the system will fail as the fish grow bigger and bigger. Most koi enthusiasts recommend 500-1000 gallons PER FISH, along with advanced filtration including settlement chambers, advanced filters, skimmers and MULTIPLE bottom drains to keep waste moving. They also ideally, like an 8 foot deep pool to keep the koi in.

I have a 2000 gallon, three foot deep pond with a DIY filter. I would NEVER entertain the idea of keeping koi in my pond. It just wouldn't be healthy for them and I wouldn't be able to stand treating the ulcers and health issues that present themselves in less than ideal circumstances.