Before Hydrotops went AWOL a few years ago, loads of good growers I knew swore by bactivator, it was credited with many health benefits and possible inoculation of hydro systems against the dreaded pythium. No known downsides or disadvantages I ever heard of.
FFF was also very highly rated by growers, I managed to get some of the last stock before they disappeared and I moved over here, but then promptly lost it. People i know well said it increased water uptake and yield, again, no known disadvantages.
I spotted that Hydrotops was back in business a while ago, and that these products are again as available, thanks for the reminder, I am off to stock up...