High TDS/DI usage

[TheEngineer]

Here's a handy calculator you can try too:

https://www.hamzasreef.com/Contents/Calculators/CO2DIDepletion.php

 

[Stopher.Stevens]

Just a couple of questions. Do you flush the membranes at all? Do you bypass the first few gallons of water to lower TDS before running to the DI?
Do you know what kind of pressure your are getting to the membranes as with 700 tds well water your Pre filters are more than likely glogging quickly and lowering your psi.

I don't flush the unit before I start, I just usually turn the booster pump on and let it go. I change the sediment filter monthly. The Carbon blocks need to be changed. I ordered new ones Tuesday night. I should have them tomorrow.

 

[Digby57]

I feel your pain! I was in the same boat, sorta. I'm on a well in Florida, and I was burning through DI resin like crazy. My tap only measures a TDS of about 180, but that's after a well maintained softener with a separate iron unit. I figured it was CO2 after being pointed in that direction after posting a similar question. I was getting about 70 gallons out of a batch of resin, and that was keeping it strictly at an output of 0 TDS. So I called BRS (where I had bought the unit and a LOT of resin) and they told me to let it go to an output of 2-3 TDS. I did not really like that answer.

Now, I think there is a lot of good advice here, but two things. I had bought all my resin from either BRS or MD for a long time. Then I happened to buy some from Premium Aquatics to get to free shipping. You can all frown on this if you want, but the stuff I had received from MD and BRS was basically identical and gave me identical results over the course of many 100s of gals of output. You know, it's mostly blue but with a lot of brown "spent" beads in there.

I was surprised at what I saw when I opened the first package I got from Premium. It was totally blue. I mean not a brown speck to be seen. I didn't think a whole lot about it, but I was used to getting 70 gals from a package and I'm now on 180 gallons on the first package of 3 I bought. I estimate that I will get another 20-30 gallons out of this first round.

I make ~20 gallons at a time and I use about 10+ gallons per week. I have 2 nanos and a freshwater tank. I'm going to be ticked if I open the next of the 3 packages I bought and see that it was a fluke that this one was so blue, but if that happens I will post it.

The other advice I have is to make as much water at one time as possible. I found early on that this extended the life of the resin somewhat for my situation.

It's all basically the same price no matter where you get it. I won't buy it anywhere else as long as I find it's consistent with this first package. And no, I don't buy anything else there and I don't work for them. I was buying a heater and some pellet food when I happened to buy this resin, but maybe I should buy more from them after all.

 

[Opus]

I have to look this up every time this question comes up... I'm going to finally put this on my website so I don't have to keep searching for it.

A standard vertical DI canister has the capacity to remove approximately 6800ppm of TDS. So if you are getting 50ppm out of your RO, your cartridge should give you 136 gallons of 0 TDS water. The actual capacity varies by the type of DI resin, but this is a good approximation. That leads me to think this is a combination of higher than expected TDS from your RO membrane as @redfishbluefish said and another contributing factor, possibly CO2.

The formula I've always seen is different from that. My calculation comes up to around 89gal of water based on a tds of 50.

 

[TheEngineer]

The formula I've always seen is different from that. My calculation comes up to around 89gal of water based on a tds of 50.

It depends on the brand of resin. Like I said just a ballpark :) Both your number and mine are higher than the OP is seeing, which leads me to believe there is another source of ions other than what is being seen by the TDS meter.

 

[Digby57]

That's interesting. I've never seen those numbers or even tried to look up an exact number for the TDS that a volume of resin should remove. Since my RO puts out 2ppm I should get way more than than 200 gallons then. Like 2000 gallons!?

So does this prove a high amount of CO2 is in my well water? What other ions can be in well water that aren't measured by a TDS meter?

 

[AZDesertRat]

I have found with most resins the number is closer to 3000 total TDS removed per pound or 16 oz of resin. A properly packed standard 10" DI holds about 20 oz. Some go as high as 6000 TDS removed but that is pretty rare. These numbers are approximations and not chiseled in stone and every water condition and resin are different so it is a rough guide only.

Unfortunately the absolute best thing you could do for your membranes is something you choose not to do and that is softened water. Even though you rent you might look at renting a Culligan, Rayne or other softener, they might do a month to month service? You would be amazed at the difference.

Lets do a little troubleshooting. What is your tap TDS, RO only TDS before the DI, your water temperature and what pressure are you running the booster at? What is the calcium carbonate hardness of the tap water? What is your exact measured waste ratio, not what someone said it was? What RO membranes do you have and how old are they?

You can get a good idea of your CO2 level if you know the alkalinity and pH of your tap water using the nomograph found here: http://spectrapure.com/frequently-asked-questions#calcc02 . That link also shows you how to build a simple PVC degassing column to drive off excess CO2 between your RO membrane and DI filters. You can also buy a CO2 and hardness test kits here: http://spectrapure.com/TEST-KITS-METERS/CHEMICAL-TEST-KITS

 

[Digby57]

Sorry to the OP if I'm getting off topic but I think this is relevant to your original question. I was pretty excited at the idea of a CO2 off-gassing unit, but after looking at that link I don't understand how the pressure necessary to get the RO water through the DI could be maintained with the air vent. I'll research this idea more for sure.

 

[TheEngineer]

Sorry to the OP if I'm getting off topic but I think this is relevant to your original question. I was pretty excited at the idea of a CO2 off-gassing unit, but after looking at that link I don't understand how the pressure necessary to get the RO water through the DI could be maintained with the air vent. I'll research this idea more for sure.

DI doesn't need pressure. I gravity feed through mine.

 

[Digby57]

I never would have guessed that. I'll have to try this.

 

[AZDesertRat]

DI is gravity fed, no pressure is required. The easiest way is mount the degassing column below your RO membrane and let it gravity feed down through the column and into a storage barrel or bucket. Once the RO is degassed you can either use a small powerhead to slowly push it through the DI cartridges or mount them below the RO storage container and gravity feed them, the slower the better with lots of contact time. I have seen photos of nice degassing set ups mounted on a stand so everything is gravity feed from the storage above it.

This is why you will notice lots of times the DI canisters do not appear to be full, the water is not under pressure.

 

[Digby57]

Well, I'll try to YouTube it and then I'm off to the hardware store after work

 

[DBR_Reef]

I would call or contact buckeye hydro- they are always helping folk on reef central, but I don't think they are on here. But I do have a suggestion myself. I assume that the second ro membrane is being fed off the waste line from the first membrane? They are usually set up this way because it saves water, but it actually increases the product water tds. But another option would be to place another booster pump on the product water of the first ro unit and feed that to the second membrane, if you get 95% rejection your water going to the di would be approximately 2 tds. It will use a lot more water though. You may have co2 issues as well, but you certainly have tds issues, so I would fix that first- you can always add a degassing tank between the first and second unit without any added pumps needed later.

 

[Stopher.Stevens]

I would call or contact buckeye hydro- they are always helping folk on reef central, but I don't think they are on here. But I do have a suggestion myself. I assume that the second ro membrane is being fed off the waste line from the first membrane? They are usually set up this way because it saves water, but it actually increases the product water tds. But another option would be to place another booster pump on the product water of the first ro unit and feed that to the second membrane, if you get 95% rejection your water going to the di would be approximately 2 tds. It will use a lot more water though. You may have co2 issues as well, but you certainly have tds issues, so I would fix that first- you can always add a degassing tank between the first and second unit without any added pumps needed later.

I'm actually feeding both membranes with water from the pre-filters. I'm not putting the waste water thru the second membrane.

 

[DBR_Reef]

I'm actually feeding both membranes with water from the pre-filters. I'm not putting the waste water thru the second membrane.

Well that increases production rate, but if you don't need that much water I would feed the product from the first through a booster pump and to the second membrane to improve the tds

 

[Stopher.Stevens]

Well that increases production rate, but if you don't need that much water I would feed the product from the first through a booster pump and to the second membrane to improve the tds

I'm not concerned with production. Just trying to make the unit the most efficient I can.

 

[Opus]

I'm not concerned with production. Just trying to make the unit the most efficient I can.

If that is the case, then I would scrap the 2 membrane setup and get the spectrapure 99% rejection rate RO membrane.

http://spectrapure.com/FILTERS-MEMB...-SpectraSelect-Plus-Tested-90-GPD-RO-Membrane

At your current 700 tds, that membrane should get you down below 10tds after the RO membrane. Also, do whatever AZDesertRat suggests. He is the guru.

 

[DBR_Reef]

I'm not concerned with production. Just trying to make the unit the most efficient I can.

I would use a booster pump then- should get you a combined rejection rate of at least 99.8% http://www.ebay.com/itm/AQUATEC-884...421-TRANSFORMER-1-4-PORT-SWITCH-/181847509792

 

[DBR_Reef]

If that is the case, then I would scrap the 2 membrane setup and get the spectrapure 99% rejection rate RO membrane.

http://spectrapure.com/FILTERS-MEMB...-SpectraSelect-Plus-Tested-90-GPD-RO-Membrane

At your current 700 tds, that membrane should get you down below 10tds after the RO membrane. Also, do whatever AZDesertRat suggests. He is the guru.

Spectrapure membranes are just dow filmtec membranes re badged. Take the 99% rejection membranes- they actually have a minimum rejection rate of 96% from dow (99% is the target). Spectrapure buys a lot of dow membranes and sells the ones that test best as their select membranes- which probably means you should never buy one of their regular membranes because they have probably grabbed all the best ones and labeled them select (That is just a guess though).

But even if you buy the select there is no guarantee it will hold that performance. The unit he is currently running uses the dow membranes already, so he probably wont see any lasting performance increase.

 

[Opus]

The OP is already using a booster pump. AZDesertRat is using the spectrapure 99% membrane and I think he recently said he is still seeing 99% rejection after 5 years of use and he has very high TDS from the tap.