I second that. Op, you have to remove the dead roots and the slime too. The bioslime protects the bacteria from normal levels of the disenfectants and you're only going to fight a losing battle.
PHYSICALLY remove the slime and dead roots from the plants and soak them for 10 minutes in physan 20 per the bottles instruction for cuttings.
Next you have to take EVERYTHING apart of your setup with no plants in it. I mean everything. Remove all slime physically. Next mix up a batch of physan 20 at 1.5oz per gallon of water and spray everything down, wait 10 minutes and wipe it down. do this twice. Follow all safety and precaution instructions on the bottle. You can try soaking any airstones in this solution if you can' take them apart but if you can't take them apart you're better off throwing them out and using new ones.
Now that there's no slime and that everythings been sterilized with quartenary ammonium compounds you can refill and dose to 1ppm of free chlorine with bleach or calcium hypochlorite. Bleach may provide too much sodium depending on your water quality and the time between reservoir changes. Check this with a pool test strip twice a day..1ppm total chlorine isn't going to do crap it has to be free chlorine. Keep pH at 6 if you go lower you will off gas chlorine. It will evaporate/be used up so you have to check twice a day. Don't use GH pH down or any other citric acid containing products.
Tests on overhead sprinkler watered small woody ornamental plants that are chlorine sensitive showed they could withstand up to 2.5ppm of free chlorine before suffering any phytotoxicity. As for what you're doing (bottom feeding) the only tests I know of showed 4ppm threshold for phytotoxicity and I'm unsure on the plants sensitivity. If you just keep 1ppm of free chlorine your ORP should stay high enough to keep the slime from coming back. You'll probably have an ORP of ~600 as a higher EC will lower ORP per my experiments. This should be adequate.