trace minerals... good or bad...

Ok, so my 46g tank seems to be doing fine. Crabs ok, snails ok, 3 fish ok. I'm really not that good of a tank keeper because my last water change was like 3+ months ago. About half of my LR has great purple color, (came from the store like that;D) the other half has nothing. Just recently I started to notice growth on the glass (little purple spots yea!!). I haven't changed anything, lights are actually on less now because of some cyano growth. The only thing i noticed is that my DI cartridge on my water filter ran out. So that instead of 0TDS water entering the tank, now it's 3-4TDS.
Is it possible that the tank needed trace minerals that now it's receiving from the not so pure water. And if AI were to replace the DI cartridge, then should I start using trace minerals as an additive?

 

LOL yes well last time I ever changed any water was ??? 30 yrs ago This one here is a little over 14 months old and still the same water. Good water flow and proper DKH and Ca and Mag. levels will all work to keep cyano at bay. get the D.D refill and not the TDS meter all that meter will tell you is that you need a D.I refill..

 

the minerals ( metals ) from tap water are no good for a reef tank which is why a ro/di unit is used. the trace elements from a supplement are different and much needed. corals use them fast. the only way to replenish them is to either do a water change or supplement. i dose seachem trace and cant remember the last time i did a water change.

 

What's a water change???? My little 5.5 gal gets topped of daily....

 

i cant remember the last water change either, but if your not supplementing its a good way to get some elements back in the tank.