One more thing:

You are going to need at least one good FAS-DPD test kit and don't allow ANYONE to use it who isn't trained on it. It's easy to do, but easy to screw up. Regular testing will save you a fortune on chemicals, prevent a nightmare of problems, and keep your pool up and running.

Pool Forum is just the place to learn the correct chemical maintenance. We have a number of stickied thread on just that but it's all really simple--once you understand the trick.

It's all about chlorine levels and pH levels. BUT there are monkey wrenches thrown in.
Stabilizer changes the ideal chlorine levels.
Total Alkalinity is closely connected to the pH.
Calcium hardness helps protect concrete pools, but is useless in vinyl.

But reading is free!

I would rate Ted's guess of two 600lb sand filters probably better than mine of two 300 pounders--Waste is better on that stuff than me by a long shot.