I would suggest you clean up the roots by holding them over the sink and spraying them directly with 3% h202 solution. Let them foam up and then spray them down with water. Be somewhat aggressive, you want to cause the dying roots to slough off. Next gently remove any mushy or discolored roots with your fingers. If they are dying they will pull off easily. Obviously you don't want to damage any healthy roots while you do this. Now you want to let them soak in a sterilizing solution for a few hours. This can be bath of strong h202, mild bleach, or a product like physan 20.
Once the root zone is sterlized, you must address what caused the problem in the first place. I personally would drop the hygrozyme, it is known to aggravate some root conditions and obviously isn't helping in your case. Any form of organic material should be kept out of the res, period. Proper res maintenance is a must. This means water temps around 68f, 1wt air pump per gallon of water, multiple air stones, and zero light reaching the water. Deviate from this at all and you strongly invite root disease.
Sometimes even though you have air stones in the res, pockets of stale water can still form, and roots in those pockets will suffocate and rot. The fact the your buckets with the sprayers are doing fine suggests that you need better circulation in the others. That may be as simple as placing your air stones differently.
Sadly sometimes perfect res conditions still aren't enough. Should this turn out to be the case for you, there are two options. You can run a sterilizing agent constantly in the res. There are many products such as Sm-90 or dutch master Zone that do a great job. H202 is another option but does interfere with some brands of nutes. Some people simply run a little bleach in their water. Your other option is to add beneficial microbes, which will displace, starve and attack the slimy stuff that kills your roots. This is best done by making an EWC tea fortified with aquashield and ZHO powder. Sounds intimidating but it's very simple. Should you find the need to go this route feel free to ask me for the method.
The fact that you are seeing new root growth is a very good sign. Good luck!