First time DWC, Temps around 80, can be fine with Hydroguard?

So that's right, I am planning to grow outdoors with DWC. I live in a tropical country, can only grow in winter due to high temps and even so the water in reservoirs reaches 77-80F even using a fan to extract air out of the reservoir. Ice bottles is another possibility, but ultimately I'm gonna need something to avoid root rot.

I was thinking on buying Hydroguard or Southern AG Garden Friendly Fungicide (Like Hydroguard but way more concentrated thus cheaper) Yes, the issue is money, folks.

Will I be fine using Hydroguard or GFF?

Also, the GFF is going to take a few weeks before arriving to my country. Can I start adding H2O2 to my water for prevention? How much?

This is going to be my first time DWC.

I'm Dwc and honestly haven't used either. My reservoirs are smaller, about 2 gallons and I change them weekly. I grow closer to sterile than a beneficial micro biome. I don't use chlorine or anything, just general hydroponics flora trio series and rain water. And my girls have kept me happy. Be careful with that hydro guard, I've seen it almost kill 3 or 4 people's grow from the bennies just going nuts and suffocating their root systems

3.5 gallon buckets 2.5 water level (just at net pots) I'm adding about a gallon to my pots a day at week 5 from seed. You can chill this water a bit, say 66 degrees or so.
Cover the pots so the light will not heat them too