Hmmm, where to start?
Everytime I see that cloud of gas I wonder what I've killed.
I'm not sure how you're applying it but I don't think I understand how you're getting a cloud of gas and killing something.

However, if you monitor pH carefully and dont like muriatic, run your pool at 7.8.

No chlorine in three weeks? That's gonna' be a problem. I doubt your pool is sanitized.

Post a set of test results and folks here will be glad to give you some advice on making your pool a little easier to manage.