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https://www.hamzasreef.com/Contents/Calculators/CO2DIDepletion.php
https://www.hamzasreef.com/Contents/Calculators/CO2DIDepletion.php
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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 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.
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.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.
DI doesn't need pressure. I gravity feed through mine.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.
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.
I'm not concerned with production. Just trying to make the unit the most efficient I can.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.
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-/181847509792I'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.