Ok. Sounds like you're recommending I use 2 Oxydator "A"s. I think I'll start slow and use 2 catalyst in one and 1 catalyst in the other. I can increase when I get a new ORP probe. My last one fried when the tank overflowed last year. Thanks for all your help. I feel much more confident to get started now. :)The main difference is down to how long each oxydator lasts between refills. However with stronger solutions of peroxide the peroxide in the model A is more likely to be converted/ broken down due to its design. With the model D you only have the catalysts and the base to act with the peroxide. With the model A the peroxide has the whole ceramic pot which also acts as a catalyst for any peroxide that escapes into it making it a safer and due to the amount it holds longer lasting between refills.
