If it's pvc glue that you get from the sprinkler section at Home Depot it's probably toxic. Read the jar. If it says non toxic or food grade go with it. Lawn sprinkler systems are pressurized and the glue is ment to hold under 24/7 pressure. Just my two cents.
PVC glue can be toxic. And if too much is used and has pushed out inside the pipe it will break down and clog your nozzles. As far as metal in the res, if it worries you there are pvc screws you can use. I use a timer. 5min on 10min off if you have a good timer. I use a cheap one and go 30min on...
Two grams of kief per pound of real butter. Bake the kief in the oven for 8 min at 300 degrees. Then then melt the butter at low heat and add baked kief. Stir until kief has melted no longer. And there you go. I use 4 grams per pound of butter. But that's me.
Sounds like stained roots to me. If you got good looking new growth I wouldn't worry to much. And keep in mind that hydrogaurd will kill all bacteria including beneficial bacteria. I personally wouldn't use it unless there is a problem.
Happy grow.
I'm on my 2nd dwc grow and it's going great. First thing I would do is transplant them into individual buckets, 3or5 gal. I use Home Depot buckets with 6" net pots. Better to lose 1 to root rot then all of them. Make sure you have plenty of air in the water. My res temps are constantly going...