Help Needed, Diatoms

[Mikelush78]

Ok I have been battling what looks like Diatoms for about 3 months now. I have had it and need to take action again to try and resolve it, but need some thoughts from the experts.

I went from my 90 - 180 gallon reef 5 months ago. My 90 gallon did not have this issue. It started about 2 - 3 months after I moved to the 180. Its a light brown algae that starts out growing on the sand and as it gets more of a foot hold it moves up and starts affecting corals. My LPS corals wont open up all the way now.

Some things I have done to fix it were, cover the aquarium for 3 days and have no light. When I do that corals come back half to fully out and then about a week I am back to the same issues again. I have found that if I stir the sand once a day it helps a bit since the Diatoms on the sand have to get their foothold again before they bloom faster but that is just delaying the inevitable.

I dont over feed, and I cut back on the lights. I have LED and I downed them to 50% and cut back the time so they are only on for Blue - 9hrs, and white 7hrs.

My water parameters are:
Calcium 420 ppm
Alk 10
Phosphate 0
Nitrate 0 - 5 ppm
PH 8.3
Silicate 0
Magnesium 1410 ppm
Temp 79
Salinity 1.024
TDS after RO-DI is 14 ppm - Think this must be my problem?
TDS Last Month after RO-DI was 12 ppm
TDS of Fresh water before RO-DI - 135 ppm

I changed my filters for my 4 stage RO-DI

I have started to have Coraline growth and my Acropora that I have had for 3 months now has doubled in size. Everything is growing great but LPS corals now... Once the Diatoms get going good int he aquarium I see them start affecting the Monti and other SPS corals...

I chagedmy filters on my 4 stage RO-DI:
RO Membrane was 7 years old, replaced it on 2-17-2013
3 Stage Filters replaced on 11-11-2012

My only thought is that it must be the TDS, Should I upgrade to a better RO-DI unit? I have had this for 8 years now. Or just replace the 3 Filters and see if that helps? May be my new RO membrane is bad? Not sure where to go with this....

Any thoughts would be appreciated...

A link to more info about my aquarium + Pics is here:
http://www.aquaticlog.com/aquariums/mikelush78/1

[Fizz71]

7 Years is far too long for a membrane. If you have DI resin on there you should have 0 tds. Otherwise you're probably burning out the DI in a matter of weeks since DI is designed to knock out the last little bit the RO doesn't get...If you have 14 after the DI I wonder what you have BEFORE it (after the RO).

Buying a new RO/DI is useless really...it's about the filters, not the plastic unit. So if you replace all of your filters (including the RO and DI resin) you basically have a new RO/DI unit.

Unless your flow restrictor is bad there is really nothing else on an RO that can fail that would produce bad water.

[Mikelush78]

Thanks Fizz, Just saw what you are talking about. My RO membrane was so old that it exhausted the DI way to fast... Haha, did not see that on my own. Thanks again.. Getting new filters set...