Well it looks to be diatom outbreak. Its caused by a spike in nutients. I would check nitrate and phosphates and cut back on any feedings and a good healthy water change.
The tank is almost 2 year old I cant believe its still diatoms. How many percent are you confident its diatoms? I have RO DI but cant remember last time i changed the filters.
Do you have a TDS meter and testing kits, you could check the RO water you are producing. If you can't remember changing the filters they might not be removing everything that they should be any more.