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My PMDD modification, acetic acid

A while back, I asked about using acetic acid (vinegar, 5%) 
in place of the HCl to prevent mold.  I wodered for two 
reasons, availability and safety.  Well, no one could come 
up with a reason it was a bad idea, and a chemist friend 
and I talked about it a bit and couldn't come up with any 
negatives, so I gave it a shot over the last few months.  

The short of it is, it works like a charm.  

The long of it is, 5ml of vinegar to 400ml of dilute 
prepared PMDD (for an automatic doser) will drop the pH 
down to about 4.2 (YMMV), and that is plenty low to stop 
just about everything.  I've seen no negative effects, 
and no precipitation.  I started out at 15ml and worked 
my way down.  At 15ml I saw precipitation but no mold.  
When I hit 4ml I saw some mold, but no precipitation.  
One more try at 5ml seems to do the trick.  No precip, 
no mold.  If you have a pH meter, or can measure low pH 
with your kits, you can probably tune your own mixtures.  
Anything below about 4.5 and above 4 seems to be about 

On a side note, I called Homegrown Hydroponics, 
(http://www.hydroponics.com/info/aquatics/pmdd.htm) and 
they were great.  Had everything for PMDD available.  Send 
out the stuff I needed dirt cheap via UPS. Arrived in 5 
days.  Couldn't be happier.