By "coral sand" do you mean "crushed coral", which should look like pieces of broken up coral and shells? It should be much bigger than sand, in order to be easy to keep inside the filter (but perhaps there's a technique I don't know about with a very fine cloth bag or something..) Anyway, assuming its the rougher crushed coral, here's the bits of lore I've read on TFF:
You should always start with a small amount, the usual recommendation being a small pile in the palm of your hand, not a full handful, but not a tiny amount either. Ideally it should go in a mesh bag if you need to keep it separate from whatever other media its in with in the filter. This is important because you are going to have to pull it out during some of your regular filter cleanings (perhaps every cleaning if they are monthly or so.) You pull it out and examine and rinse it in order to get the debris and even bacteria off of it, otherwise it will clog up and not continue to dissolve into the tank. (This is of course in direct contrast to your other biomedia, like ceramics or sponges, where you want to take great care of your bacteria.) With the crushed coral you can even clean it in tap water, something you would never do to your biomedia (assuming of course the you still have plenty of biomedia and haven't made your coral a significant percentage of your filter media, which you shouldn't.
You need to be aware that it is very slow. It may not do anything to your pH for 2 or 3 weeks, but you should keep testing periodically and eventually decide if you want to gradually increase the amount of crushed coral a bit. Always make these increases fairly small and then give it weeks of testing to decide whether to increase or stop.
By my readings, crushed coral is the most highly recommended (here on TFF) way to preceed to raise your pH with fish in the tank. Purpose-sold chemicals are faster, and there are those that say they are ok, but many comment that its easier to get pH swings with chemicals and swings that are bad enough to be bad for your fish. Baking Soda certainly does the job accurately and is cheap, but it is also the fastest and goes away quickly, so takes even more careful monitoring - almost impossible not to have a mistake eventually with baking soda. I think baking soda is the method of choice for fishless cycling -- for that function its fast and accurate and then you can get rid of all of it at the last big water change before fish.. so its wonderful for fishless. But for fish, its too risky in my opinion, just because of human failings.
~~waterdrop~~
ps. Amunet, some day I want to meet that cat.
where do i put it in my tank's filter though? im using the aqua one 620.. its about 20 gallons and so far theres only 2 albino corys in it. 
