Checking with a tds on RO maybe not enough as I just learned.
TDS checks for solids and
Silicate will not show up well on a TDS meter unless the pH is high enough to form silicate (Si(OH)3O-; pH above about 9). Otherwise, it will mostly be in the form of silicic acid, Si(OH)4, which is not conductive.
Therefore, if you have an algae problem could be that your high on Silicate which I am. I got my RO water tested by a lab and a whopping 506.8 µg/l and my TDS showed zero.
Get a test kit to check for Silicate like Salifert. I am going to make a video of my results soon.
I am going to try different methods to see whats best for my case. RO/DI it will have different results based on everyones water supply. The issue with Silcate it's hard to remove from RO alone so you may need a special resin or 2 or 4 DI to get it to 0. Spectrapure makes Silicon Buster
My current system has this:
1 micron sediment>1 micro carbon> 1 micron Chlorguard> 98% Membrane > Mixed DI Resin with this I get 506.8 ug silicon still getting through system. Ouch
I am going to change it to:
1 micron sediment>0.5 carbon>1 micron Chlorguard>99% Membrane>Silica Buster> Mixed Di Resin that is my plan.