Diatom/Silicate problem

[FargoReefer]

Hello,

I have a 240 gallon reef tank that has recently developed a problem with diatoms. I did some research and found that diatoms feed off of silicates, once the silicates are gone the diatoms are gone. So I went out and got a TDS meter and started testing water. My city water is pretty bad having a TDS reading of right around 1000ppm. I then tested my RO/DI water and noticed it was right around 200ppm, which I think is still too high. I recently bought a change of filters for my Kent Marine Hi-S 60gpd and tested that water. The TDS reading did go down but not as low as I expected, it dropped to about 30ppm. I have read that other people change their RO/DI filters when the TDS reading gets above 0ppm. I also checked on the Kent Marine website and found out that my RO/DI unit is optimized for TDS lower than 200ppm. So my question is can I simply put some sort of pre-filter in front of my RO/DI or do I need to get a new RO/DI system? What are my options for fixing this problem? If I need a pre-filter what kind of filter do you recommend and if I need a new RO/DI what brand/model do you recommend?

Thanks for the help!

[lecher]

Did you replace the RO membrane as well? Have you measured the waste water to product water ratio? Should be about 4:1. If not, might need to replace/adjust the restricter. Whats your water pressure? Pressure should be at least 40psi at membrane. Most people including myself get 0 TDS. Something is not right. Spectrapure has a add on MaxCap double DI canister filter which might would help further polish the water. Although 200 TDS going into it woulb prob. deplete the DI filters pretty quick. Hope this helps. Good luck.

[FargoReefer]

No I didn't replace the membrane, but it is on order, should be here in a few days. I haven't measured the waste water to product water ratio, how would i do that. Just compare the amount of waste water created in a minute vs the amount of product water in a minute? I have a booster pump as well so my pressure is pretty high, around 85psi. Is that too high?

Thanks for the replies!

[demonsp]

Whats the tanks age?
Whats used for water flow in there?
Water change amount and scedule?

[lecher]

Yes waste water is determined by measuring both product and waste over a certain period of time, 1-2 mins would be fine. The ratio is changed by changing the length of the restricter. So if it is to short now you might would need a new one.

[Randy Holmes-Farley]

The effluent from an RO/DI should read 0 ppm TDS. If it reads higher, then it is malfunctioning or depleted, and lots of silicate can get through. Silicate is one of the easiest things to get through a depleting DI.

Did you measure the TDS when you first replaced the DI resin?


This article has more on silicate getting through on depletion, and on when to replace filters:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

[NaH2Ofreak]

If it were me, I would just go to SpectraPure and fire off an email to them. They could tell you EXACTLY how to solve the problem. While you're there, ya might want to look into a MaxCap RO/DI system. Works like a charm!

Dennis

[Buckeye Hydro]

<a href=showthread.php?s=&postid=12091948#post12091948 target=_blank>Originally posted</a> by FargoReefer
Hello,

My city water is pretty bad having a TDS reading of right around 1000ppm. I then tested my RO/DI water and noticed it was right around 200ppm, which I think is still too high. I recently bought a change of filters for my Kent Marine Hi-S 60gpd and tested that water. The TDS reading did go down but not as low as I expected, it dropped to about 30ppm.

Remember that it is only your RO membrane and DI stage that reduce TDS - so although you may have needed new prefilters - they won't change your TDS readings.

We need TDS readings from three locations - you've provided two:
Tap: 1000 ppm
RO: ?
DI: 30 ppm

We know your pressure is good at 85 psi - you can adjust that up to a max of 90 psi and improve performance a bit. Where is the pressure gauge in your system?

Even if we get you to a situation where your membrane is operating well, because your feedwater TDS is so high, you will go through DI resin relatively quickly. You would be a good candidate for a system with at least two DI stages.

Russ

[FargoReefer]

Thanks BuckeyeFS! I wasn't sure exactly which filters took out TDS.

Here are TDS readings from the thee locations you mentioned:
Tap: 1000 ppm
RO: 342ppm
DI: 30 ppm

I do have a replacement membrane on order and it should be here in the next couple of days. Now from those readings do you think that my membrane is bad, or is my membrane preforming as expected with source water at 1000ppm of TDS? It looks like it is removing appox. 650ppm of TDS, and my DI filter is doing the rest to get it down to 30ppm.

[lecher]

A good membrane will reject 95% +. So I would say that the membrane is shot.

[Buckeye Hydro]

You are only getting a 65% rejection rate. So either your membrane is bad, or it isn't seated properly. What is your waste water to permeate ratio?

Russ