reverse osmosis troubles, di exausting too quickly

[TamiW]

I am having trouble with my ro/di water and I'm at my wits end. My di cartridge exhausts after maybe 100 gallons, at most. I've got rather hard water with tds of almost 700 out of the tap, and it comes out of the ro side before the di at between 8 - 12 tds.

It was higher, but at the suggestion from a previous thread (I can't find) I added a ro pump, and the water was going in at 35psi, but now it goes in at 65psi. I tried a new RO membrane thinking it was faulty, but research suggests that actually with the 98% rejection rate, my TDS is where it should be after the membrane.

The problem is, I burn through di. And I don't know what my next step is but I can't afford to be changing DI that often. So is there anything else i can do? Would a second ro membrane reduce the number further, or is what's getting though going to get through no matter what? Any other ideas?

The unit is from ebay, its got three pre-filter cartridges, the ro membrane, then a horizontal di unit. The ro membrane is a dow filmtec 75 gpd. I have well water and have a water softener and an iron filter before the ro unit.

Any thoughts on what I can do to fix this would be appreciated, because I'm at a loss.

 

[Pyrrhus]

Horizontal DI is a very poor method of DI usage, you really, really want to have a vertical DI unit.

Even with a vertical DI unit you will be getting around 200-250 gallons of pure DI water before replacement with your typical DI cartridge or refill.

Your membrane and prefilters sound like they are running fine, boosting your pressure was a good move.

If you really want to get the best lifespan possible out of your DI resin you should look into the Spectrapure Maxcap add-on units, I promise that you will get significant DI savings over any other DI on the market.

Ditch the horizontal DI and replace it with one of these units, you should get upwards of 600-1000 gallons of water before you need to change the first DI cartridge.

http://www.spectrapure.com/St_MaxCap_D2.htm

If you want to get some reviews on this system, stop by the FRAG forum in the club forums, there are a ton of AZ reefers that use them and we have similar water issues.

 

[luther1200]

I agree that you should get a vertical DI. The horizontal ones "channel" and thats why they are getting exausted quickly probably.

 

[TamiW]

Thanks. I don't disagree I need to get the vertical one (I've been meaning to anyway.) However, I don't think that fixes the problem. I think I need to get my TDS down post ro BEFORE the resin. That's what concerns me right now.

As for the MaxCap, I'm not sure how it makes a difference other than it ads more resin by having two units. Or is it the resin itself that's different?

 

[shaggy14]

What is you hardness of the water. Not tds, but the actual hardness. I was having similar problems except I would only get around 50g before my di was exhausted. My water hardness was over 250 and that was with a tds of 600 out of tap going through a 5 stage system. I ended up selling the unit because it was cheaper for me to just buy distilled water than to kep replacing filters and resin.

 

[Pyrrhus]

<a href=showthread.php?s=&postid=15497547#post15497547 target=_blank>Originally posted</a> by FishGrrl
Thanks. I don't disagree I need to get the vertical one (I've been meaning to anyway.) However, I don't think that fixes the problem. I think I need to get my TDS down post ro BEFORE the resin. That's what concerns me right now.

As for the MaxCap, I'm not sure how it makes a difference other than it ads more resin by having two units. Or is it the resin itself that's different?

Your RO only TDS is well within spec, there really isnt anything that you can do to further lower the TDS that I know of besides the maxcap unit.

It is possible that you have high levels of dissolved Co2 in your RO water, it isnt removed by a membrane and wont show up on a TDS meter but will exhaust your DI resin the same as TDS. You can build a device to offgas the Co2 but this is getting fairly complicated and may not make much difference. I do not know if you have Co2 in your water or not.

Maxcap is sort of a DI roughing cartridge, it removes the vast majority of the TDS before it reaches the mixed bed cartridge. You can think of it as a DI prefilter.

With your numbers, you should get 0 TDS out of a Maxcap cartridge for 600-1000 gallons or more and the mixed bed cartridge after the maxcap should be good for at least 3 maxcap changes. IE, you get anywhere in the range of 1800-3000 gallons of pure 0 TDS water on only 4 cartridges of DI, there is no other DI system on the market that can do this.

 

[TamiW]

Okay, I think I understand. Except, does the maxcap go before a normal di cartridge, or is it the normal di cartridge.

One thing I didn't think to mention above is that this really seemed to start around the time i had a new water softener installed. I didn't have a tds meter at the time but the color changing di resin lasted for a long time. I don't know how that could have affected my water, but that seems to be the time frame that I started having problems.

I'm probably going to get a co2 test kit to see if that is the problem, if for no other reason than to satisfy my curiosity.

 

[Pyrrhus]

A Maxcap cartridge has to be used between your membrane and a "normal" mixed bed DI cartridge, its an addition not a replacement.

From my understanding, the water softener is actually a good thing for your RO unit and will increase the lifespan of the membrane and the quality of the water it produces.

Perhaps the addition of the water softener coincided with a natural increase in evaporation due to seasons? I'm not sure about wells, but here in AZ our municipal water supply TDS is always the highest in summer, we get much better DI life in the winter with the lower TDS input water.

Definitely consider testing for Co2, I believe that 1ppm is equal to 1 TDS for DI purposes. I have been told that in some areas the Co2 can actually be higher than the actual water TDS.

One other thing I forgot to mention, is your waste to product ratio at least 4:1? You should be sending 4 gallons of waste water for every 1 gallon of RO with that membrane and pressure. I dont think this is going to help your TDS or DI lifespan much if at all, but it will help protect your membrane by ensuring it is properly flushed.

There is some good reading in here. http://www.reefcentral.com/forums/forumdisplay.php?s=&forumid=229