New RO/DI system acting weird

The rejection rate is 95.3% which is not very good. Dow Filmtec advertises 98% with a stabilized rejection of 96%. Those are for dry, untested, off the shelf membranes and not all will achieve that. I would have kittens if my rejection rate was only 95%, my DI replacements would quadruple in frequency and cost and I would probably give up reefkeeping.

The Spectrapure Select membranes are guaranteed to be better than 98% and I'm still averaging 99.4% after 5 years of use so my DI life is amazing. The extra $5 or $10 for the tested and guaranteed membrane is worth the initial cost when you consider how much it saves in DI over its lifespan. Spectrapure tells me they reject the majority of membranes they test for their Select series since they do not meet their standards, tahat tells me something.

Colder water will drive your waste ratio higher since it is more dense and less fluid than warm water and is actuallly better than warm water so I would not try to blend or temper hot and cold. With your 90 psi and cold water you shoule easily be able to get better than 98% rejection. I run my booster pump between 95 and 100 psi myself and use only cold water which sometimes drops to 56 degrees F here in Phoenix believe it or not.

 

I take that rejection rate is pretty crappy then. My cold water is around 70F now in the summer, at least as far as I can trust the temperature sensor of my hot water dispenser. (I guess it's a highrise building drawback...) I don't do any mixing... Hot water is for taking a bath. XD

So you're saying I do not need a pressure regulator for 90 PSI... That sounds good. Will I need to adjust the flow restrictor based on the pressure?

 

It should be better at 90 psi and 70 degree water with only 150 coming from the tap. My tap is 630 and my RO only TDS is between 2 and 3. If my rejection rate was only 95% my RO TDS would be over 31 and DI wouldn't last worth a hoot.

90 psi will give you a better rejection rate and higher GPD than 50 or 60 psi.
You could expect right at 120 GPD at 98.8% rejection rate or higher at 90 psi and 70 degrees versus 80 GPD at 98.3% rejection rate at 60 psi. That extra half a percent on the rejection rate should make your DI last 25% longer than at 60 psi which doesn't sound like much but if you make much water it adds up to a cost savings over a couple years that would more than pay for the better membrane and then some.

 

Hey,
I got my Spectrapure system, will set it up tonight... One thing, apparently the resin container has been installed in reverse (ie. the input is plugged into the end that says OUT and vice versa). Does this affect anything, or can I just leave it alone?
Also, for drinking water, does it make sense to add an organic carbon postfilter after the DI stage, or should everything be gone by then that the carbon could remove?

 

Well the system's up and running. After some reading and looking at how the system works, I flipped the DI canister so that flow goes in the factory indicated direction, as this guarantees uniform pressure throughout the resin...
I tuned the system to 4:1, I had to cut the restrictor to 10mm, and I have a product flow of 350 ml/min (~135 GPD), the built-in pressure indicator is hovering at 80 PSI... Awesome, I gotta say. Water for a 4-5 gallon nano reef won't be an issue at all I guess.

 

The DI canister was correct.
The flow in a DI goes from bottom to top so all resin comes into contact with the water. When the canister lid is reversed the flow is correct for the refillable DI cartridge unlike when using sediment can carbon filters when the flow goes to the outside then out through the middle.
Change it back, they know what they are doing.

 

Thanks for the info. XD

 

Okay I changed it back... But I'm not sure I'm clear on this. So the flow is supposed to be input in the middle, and output at the rim? How is that bottom to top?

This way as far as I understand, the water feeds directly into the top middle opening of the cartridge, travels downward through the resin, exits at the bottom, flows up along the rim of the canister, and exits through the hole marked "in".

 

Well apparently I was right in flipping it.