GH question

So, one of my tanks has been really foggy the past two weeks, did water changes, and still no change.

pH 7.6
Ammonia 0
Nitrite 0
GH 13

Would the Hardness be the problem? [I'd like to have it around 6]
I added some distilled water, I think my tap is the problem.

Could that be the problem, and is there something I can use besides a fix in a bottle? [I work all night and have stuff tomorrow, so I doubt I'll get the chance to pick something up]. Or do you just suggest picking up a bottle of something?

It's for my loach/hatchet fish tank by the way...

I'm terrible with this parameter stuff, advice would be appreciated =]

[also, the tank has been established for months, the problem just developed recently]

tank has a sand substrate, dojo loaches and kuhli loaches, syno cat, and hatchet fish

added a new rock a few weeks ago. thinking this is the source of the problem

i removed the rock, thinking it's putting calcium or minerals into the water. going to change water and check in a few days...

so i've been gradually doing water changes, and it's starting to clear up.

my guess is that the rock that I had, which I got from someone who has a million tanks, was used for his brackish tanks. it was releasing minerals like crazy in my water. no wonder when i did water changes with it in my tank they was no change. now that it's out, things are looking up