Dwc what am I doing wrong

One of my plants the leaves are very dark green and the leaves are like waxy rigid looking I use general hydro Maxi series base water is 150ppm after bites I’m at like 550 water temp 74 degrees growing dwc thanks

Water temp should be under 68.. Run a sterile system..

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I've used bleach in hydroponics (sodium hypochlorite) for decades. 3 ppm is typical with DWC. Adding the same dose every third day and with anything going in to the reservoir like top offs and reservoir changes.

It's not a matter of if but when will you get pythium root rot if you don't do any preventative measures. If you can't control the water temps you should go sterile.

Here the dilution calculator:
Chlorine dilution calculator

Good luck! You've caught on early so I think you're going to fix all of your problems.