you have algea where? Of course you need to clean that shitup everyweek bro, you shouldnt even have it in the first place..

there is a light leek in the res, algea cant survive without light...why do you think you had root rot last time? lol it was prob in the same setup...you said when the humidty goes up it happens? why are you letting it go up? get a dehumidifier and do what ever you have to do to keep temps, and fresh air circulation in check.

if your res temps are not in check, the grow room temps are not in check and you have light leaks to your res all the hydroguard in the world isnt going to save you.

posting pics of your setup would also help alot

peace