0 hardness ?

[mich]

Hi all
Apology for long post in advance....
well after posting about the red lines on my white discus in the illness section, I decided to add some melafix and pimafix to fix up any fin issues. Well all went pear shaped from there, within hours the tank crashed, PH dropped from 6.8, where it always sits to very low ? Fish not happy and some had skin and fins damaged. So quickly did water change to up PH slowly ish, fish settled down a bit. Hadnt done hardness test for a while, so did one and crap....0 hardness(KH) I guess thats why it crashed so suddenly? Anyhoo I changed a while back from Discus buffer to HCL for softening water, was working great. but i now cant get the ph down enough with it and keep some hardness for buffering capacity at the same time. The GH (General Hardness) is high about 10.
I was wondering if the buffering capacity came from the tank(substrates etc ) and now have depleted and HCL pushing down to much.?????
What do you think about using tiny amount of HCL to soften water a bit and then Discus buffer to bring PH down without softening the water further ? Or am I barking up the wrong tree completely.

Oh, I got some fungus issues on damaged skin of fish so Im running with Malachite green, second dose put in last night..fish repairing well.
PH at 6.8 / 7 now but harness still 0. I added aged tap water with no HCL to raise hardness but didnt work, raised PH as high as I want it to go though . so kinda stuck and scared of 2nd crash.........

all up lost 2 fish, one i think with gill damage through acid water ? and another which had defective bowl anyway was off centre and probs with poo i think.

What should I do to buffer and keep PH down ?

need help so i can sleep at night again !!!!!! Aaaargggg

Thanks Michele

[mich]

Anyone?

Any suggestions would be appreciated as im on the verge of trying the HCL (min amount) then discus buffer again to lower ph only. i found in past DB didnt have too much affect on the hardness just the PH but it was stable.... very costly on the big tank though, hence the move to HCL in the first place.

Just when you think, geez this is easy ! bang it gets you ! Bloody discus, wish i didnt luv em !!!!

Cheers
Mich