Im not hip with a ton of nutes since I just use FF grow big for hydro and Humboldt ginormous additive for my P & K. If the label states it has any kind of "Guano" or "worm Castings" or anything from a once living organism -its an organic nute. Basically if it has any form of "poop" in it. I looked at the gh flora series and the maxi bloom and Im pretty sure they are both synthetics which brings me to your original issue. If you have bacterial slime in your res without the use of organics, then you have another factor causing the slime like res temps being too hot(but not likely if you are at 22-24*C),not enough aeration/circulation in res, light getting into the res etc. Hydroguard can be used on both organic and synthetic nutes. I would be using it as a routine safeguard anyways whether there was a problem or not if you already have it. I just use h202 since I run synthetics and the h202/water is so cheap and readily available.