Remember, add acid to water, not the other way around. and neutralize it before disposal, a few boxes of baking soda should do it.

WAYYY off on a side note, there's many literature about adding vinegar to kalkwater to saturate the cal/alk levels. Does the same benefits apply with HCL?

Scrapped off a ton of coraline, maybe 4 or 5 lbs (not kidding either).

Tank is full of tap water now, added about 1 liter of muriatic acid to tank, ph dropped to 2.4. (330 gallons of system water). Within 30 mins ph went up to 2.8, added another liter. Then after a few hours added a few more liters. Ph is now at about 2.2. Not sure how low I should go, I will watch it over the next little while, see how it is tomorrow.

So far we cannot smell it in the house, but the skimmer is going crazy!

FWIW I bought 40 liters of muriatic acid.