Marvin, here's my approach to treating cyano:
- test the RO+DI water with a TDS meter...the shop you buy from should have one available for you to check before you buy....you need a TDS reading anywhere from 0 to 4 (FME)...any more and you should notify the staff to swap their filters, cuz you're not getting your money's worth, imo
FYI....RO+DI sold at water stores like that is primarily for HUMAN consumption..as such, it is common to have the raw RO+DI effluent (TDS at this stage would be, ideally, around 0 or 1) run through a final filter stage for 'taste' (this is
usually crushed coconut shells)...this reintroduces some nutrients and minerals to the water (TDS at this stage can be around 10 or even more!)....you DO NOT want this....confirm with your water store.
- lots of flow ...but seeing your specs, i think you're OK
- phosban reactor.....if you don't run a skimmer, then I would REALLY, REALLY suggest you install one ASAP......I run two phosban reactors in each of my tanks...one is filled with Rowaphos and the other with carbon, with each daisy-chained to each other....fluidized filters are where it's at
- use chaetomorpha as your only macro algae, and blast it with piles of 5500K light...you should be pulling out handfulls of the stuff a week... if you ain't, get more light!....caulerpa is a p.o.s for nutrient export...don't even get me started
- water changes....i don't believe in stinking water changes......the water in your tank is golden..it's well aged and mature....what i do instead, is to test like a **** and supplement with minerals on an as needed basis.
and i know it's tough, being the frag master you are, but try and keep your hands out of the tank for a bit

hahaha
good luck, mate!
Zach