Dutch Master Zone... Use it.
I have been using it(Zone) on and off. There is a gold and a black version. Unsure of the differences, as DM doesn't respond to inquiries. I have a jug of gold.
Using Ebb&Gros, and have been overwatering...the standing water coupled with a hot day and no AC really contributed to problems, particularly the plants that were getting watered in the system, which did not really require it.
The main issue I have with Zone, is that it has no recommended top off instruction, and without a measuring standard and means, doesn't allow for a very objective analysis. So when the amount is too concentrated or dilute, there is no means of knowing.
A top off recommendation is the least they can do. If you are draining to waste, it's clear how this is to be used. But for those of us using recirculating systems, if there are no topping off suggestions, or standards and means of measuring, we are left guessing and shooting in the dark.