Right -- you don't want cal-hypo and trichlor to mix, but once they are in the water, it is fine. You can use both products in a pool. Lots of people do. But, in your pool, I would just use bleach and skip the cal-hypo. You don't need the calcium and cal-hypo is slow to dissolve sometimes and can cloud the water. Stick with bleach and you won't have any problems. And, again, it is fine to use the trichlor as long as you monitor cya and pH.

Re: the muriatic acid --- Sure, find out where it is sold in your area but don't buy any yet. You may not need it, especially if you are gonna use the trichlor for awhile. In that case your pH is gonna be falling and you're certainly not gonna need the acid. Many people never need it. I have had my pool for ten years or so and have never once needed it ....... and I don't even use trichlor.