Hydroguard might actually be doing you a favor...... Give this a good read. I see a picture in this thread on another website that has exactly what you are describing. There is also GREAT info and a few links regarding slime, algae, etc. RICHYRICH's posts are very helpful...
https://www.icmag.com/ic/showthread.php?t=55259&page=2
(Second Page is where you will find Richyrich's posts.)
Here is another copy+paste quote from someone on the same forum. Not sure if you might have used hygrozyme or a similar product in the past?
"I am already using hydroguard and hygrozyme. When I put a sample of the roots into a clear plastic bag with tap water, the stuff on the roots looked white and fuzzy, kind of like mold. So I took a sample of the roots into the local hydro store, and the guy told me it looks like I might have had a bad batch of hygrozyme or that my hygrozyme possibly went bad. He thought this b/c hygrozyme is suppose to take care of this kind of problem. But seeing as it is an organic solution, it is possible that it went bad. I cleaned the rez out and cleaned everything but the plants and net pots. I cleaned the roots with a mixture of h2o2 and water @ a concentration of 20ml h2o2/gal.
Started a fresh bottle of hygrozyme."
Hope that helps!
Read my thread!