I got a cup of aragonite from a friend and I was wondering how much of it should I add in my 75G to raise the kH. The Kh in the tap water is <3

1/3 cup of crushed coral for my 90 gallon gives me about 6-7 kH. This is starting with very soft water. From what I have seen, this will build up over time, so the 50% weekly water changes help to keep it down.

I think Aragonite is quite similar to CC, but am not sure.

couldnt u just use baking soda???? to raise the kh

That would be temporary and I would need to add baking soda every now and then. Aragonite/Crushed Coral is more permanent.

oic cool that makes sence