I was under the impression silicates will not show up on a TDS meter.
I've heard conflicting info on this. I suspect it to be true...
IME, my first tank had an ongoing diatom problem. I would do WC and vacuum them out but they would be back in full strength the next day.
Once I moved the corals over to my new tank and started to neglect WC on the old tank, the diatoms begun to die back (and the new tank had a massive bloom). After this I started to consider the source water and added an extra cartridge with GFO as the last stage on the RODI unit; and after a couple of weeks the diatoms disappeared.
While I never tested for silicates, I received a triton test this week that says I have far too many of them. There is also a small patch of diatoms growing on the sand so I'd say the GFO needs to be replaced.
If your source water does contain silicates, the tank will get a steady supply from evaporation top off and water changes. If they don't pass on in a couple of weeks, take note of their growth (eg. do they come back strong after a WC?) and perhaps skip a WC to observe if there is any change.
Exactly, I run a silica buster cartridge as the last filtre before it hits the tote.
This sounds much better - anyone know where to get one in AU?