I've had troubles with WW and distilled water too. Rusty/pinkish residue covering everything in my loop. I used about a capful of WW to 1-1.5qt of water. There were no temp improvements that I could detect. I used a solution for cleaning my humidifier to get it out. Circulating a mixture of cleaner and water thru my loop for about 1/2hr does the trick. Also I rinse by circulating clean water thru it all a few times before reassembly. I've come to the conclusion that there is no reason for me to use WW if there is no aluminum in my loop. To control growth in my loop I add a bit of bactrostat that once again is made for my humidifier. If you are interested in these, check any place that sell humidifiers, I use Holmes brand products. The cleaner is acidic so be sure and flush it out of your system.
edit:
Here's a link to
Batrostat and
Cleaner.
peace.
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