One of the "two forms of nitrogen" in Thrive+ is urea. In PH of 7 and below the urea is in the form of ammonium which is harmless. As the PH climbs above 7 it starts to turn into ammonia which can be toxic at high levels.
It's not an absolute thing where at 7.1 it all becomes ammonia. That's just where it begins to happen. Probably not a big deal unless the PH is in the upper 7s and above (temp also plays a role), but that's why it's recommended for PH levels under 7.
Besides that, Thrive+ has twice the Fe. That's the main difference. I believe Fe in both versions is EDTA
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