You might be better off running the Abyzz pump as an external. They run pretty cool so there isn't much heat transfer, but even at low amperage, that's 400v in saltwater you are exposed to. I use larger Banjo brand all stainless clamps. I'm using silicone hose, but would use braided in the future as it is less likely to split or cut.
The carbon dosing is definitely the cause of the cyanobacteria. I would discontinue it and use erythromycin phosphate (250mg/10 gal x two doses, two days apart). Red Slime remover switched to a non-phosphate erythromycin and it doesn't appear to work anymore. There's more phosphate in a single tank feeding, so it's a non-issue. Remember to turn off skimmer, o3, UV, and chemical media. Turn skimmer on conservatively over a 3-5 day period as carbon removed the E.M.
Turning down the white lights and relying on blue light will not stress the corals too much and help fight the red slime.
I use a small brine shrimp net and a baster to physically remove as much red slime as possible, as it is toxic as it dies off.