Changing DI resin monthly

[winland]

I live in the country/farmland and have well water.
My TDS right from the well is in the low 400's.
It is about the same after the water softner.
After the RO it is about 40.
It then goes thru 2 DI canisters (large) and normally comes out zero.
But I have to change the DI resin ever 4 weeks to keep the TDS at zero. By the end of the 4 weeks, the TDS is going up to 10 - 15.
Any ideas as to why?
As I said, I do live in the country in the middle of a bunch of corn/soybean/wheat fields. I know that my well has lots of nitrates in it, but after the RO/DI, I never have any testable nitrates.

Why do I have to change my DI resin so often, or should I let the TDS go higher before changing?

winland

 

[Randy Holmes-Farley]

How many gallons before a change?

The DI should be replaced as soon as it rises above 1 ppm TDS, IMO.

 

[bertoni]

The RO membrane is not doing all that well. Is it a 100 gpd model? If so, I'd substitute a good 75 gpd membrane. The output should then be about 10 ppm in TDS, which would help a lot.

I would change the resin as soon as the TDS started to rise:

http://reefkeeping.com/issues/2005-05/rhf/index.htm

 

[winland]

The TDS is Zero for about 3 weeks and then starts going up.
It is a 100gpd RO/DI unit.
I probably make about 250 gallons of Zero TDS water during that 3 week period prior to the TDS starting to go up.

winland

 

[atvdave]

A 100 GPD Dow Filmtec membrane has a rejection rate of 90%. If you got it from e-bay it's probably less. ( I know cause that's what I did)

A 75 GPD Dow Filmtec membrane had a 98% rejection rate.

So at 400ppm 90% = 40ppm after the membrane
at 98% 400ppm = 8ppm after the membrane.

Also what type of DI canister do you have? If it's the horizontal type I'd replace them with the vertical type like in the link below.

http://www.buckeyefieldsupply.com/showproducts.asp?Category=39&Sub=127

 

[winland]

I am using the 100 GPD Dow Filmtec membrane.
I am using a vertical, dual DI canister, similar to the one on Buckeyefieldsupply BFS-267 Double DI kit

My TDS measurements are confirmed with 3 different TDS meters.
All read generally the same PPM.

winland

 

[reef_doug]

I think the problem is the 100 gpd membrane which are normally only 90% rejection. Thus your 40 ppm after RO is correct, but poor product water in part of the high source. 40 ppm will burn through DI fairly quickly, yes DI may lower it to 0 but it will be exhausted very fast and creep up shortly.

The solution would be a 75 gpd membrane with 96-98 rejection ratio to bring your post RO water to 16-12 ppm. The hand selected Spectrapure membranes are really good. Your DI will last longer and save money in the long run.

When changing membranes, also get a new flow restricted to match the new one.

Good luck.

 

[reefkeeper2]

You mentioned a water softener. I also have a softener. Your softener takes out stuff like iron and manganese and exchanges it with sodium. The RO membrane cannot remove sodium, so your DI resin is quickly exhausted. This is how it was explained to me (can't remember by who, maybe Randy). I reworked the plumbing so the ro/di unit gets water straight from the street, before the water softener. This adjustment makes your membrane work harder, but spares the di resin.

 

[bertoni]

Actually, the water softener will help the RO membrane since the sodium can be filtered, and won't cause deposits the way calcium can.

I agree that a 75 gpd membrane is a good idea. What type of DI cartridges (brand, resin type) are in use? I need to do the math, but I think they should be lasting longer if they're full-sized 10" cartridges.

 

[Thefilterguys]

You are getting exactly what you would expect from a 100 GPD Filmtec membrane 90% rejection. Tap water tds 400 x 90% equals RO tds of 40. A full sized DI cartridge will absorb 5100 ppm of tds if you have no CO2 issues. Two cartridges would give you about 250 gallons and you would start seeing a reading. DI resin should be changed out at no higher then a 2-3 reading at best. The better way to run a dual DI is to use color changing resin and when you start seeing color change in the second cartridge rotate a new cartridge into the second position and move the second into the first position. You will always produce zero tds water. Given you high tds I highly recommend going to a Filmtec 75 GPD membrane as suggested.

Jim

 

[bertoni]

Thanks for doing the math!

 

[Thefilterguys]

Jon I think the math was already done more then once just wanted to confirm he was getting expected capacity out of his resin.

Jim

 

[rbursek]

Jim, that is why you guys are the best!!!!! Getting any snow tonight?????? Bob in Germantown 14-20" but it really is not happening yet to get that!!!!
Bob

 

[winland]

Thanks for all the great info and suggestions.
I guess I will be going with a 75gpd membrane in the near future.

thanks again,
winland

 

[rbursek]

Also change your orifices for flow rate, talk to Jim at The Filter Guys

 

[Thefilterguys]

<a href=showthread.php?s=&postid=11776633#post11776633 target=_blank>Originally posted</a> by rbursek
Jim, that is why you guys are the best!!!!! Getting any snow tonight?????? Bob in Germantown 14-20" but it really is not happening yet to get that!!!!
Bob

Sounds like you got a good dump someone said 30" and we got a dusting.

Jim