I had the same problem with my cloners and eventually gave up on them. Have 2 in a storage pile and another NIB. Did find some success with an antibiotic but wasn't worth the hassle. Ended up just using rockwool plugs & trays from the hydro store; more foolproof & usually 100% success rate.
Here is another part of the upgrade... 3 net pots instead of one. It helps keep the activated carbon dry, by raising the net pot that holds the media, out of the water.... Which makes for better 03 absorption (as this is a dry air filter, and the type of activated carbon being used, is optimized for dry air filtration, rather than wet water filtration).
Here is another part of the upgrade... I added a proper air pump to push air through the dryer and through the ozone generator.
Even though I have a Venturi that is sucking the air, I don't feel that it is efficient enough... The dry air needs to keep moving through the ozone generator, or nitric acid can form, which lowers the pH of the water.
Finally, before the upgrades, I checked the flow into the reservoir and it was 4 gallons per minute... Simply not enough.
Indeed, I needed to install the other 700 pump that came with my second 8 XL system.
I installed both pumps in parallel, and installed the splitter after the pumps, which then ran into the chiller.
The flow then improved to my targeted 8 gallons per minute.
Here's one that got done early,... The only Critical Kush.
I hooked up an air hose, put a small pump inside that recirculates the water and sprays it on top from above, and flushed it with Flawless Finish for one day.
I dumped the Flawless Finish, and am now flushing it for another day or two with RO water.