I think you bring up a valid point. I think I read my Tds wrong. I should be 1 not 0.01. After collecting another 20 gallon it is 4 now. I just replace di resin so I think my membranes need to be replaced. Thanks for all inputs

I have done that, and the water line just goes down again. What I don't understand is that from what I can tell, my DI cartridge works like a Phosban reactor where the water goes in the top of the cartridge and comes out the bottom of the cartridge, then flows up to the top of the chamber where it leaves the chamber through the top plate. That's what it looks like to me, so how the heck is there water coming out of that chamber when the outlet is as the top and the water level is only halfway up the chamber? I get about 12 ppm out of the RO, and 0 ppm out of the DI.

Myka
I think it must work like mike31154 says. Water comes in on the outside of the DI canister and then exits up through the DI. That way, air cannot escape easily.
I think if you reverse the flow(don't know if its any better) to go into the top of the DI cartridge and exit the bottom and then out of the cannister, I do not see any possible way for air to stay in the cannister.

so here is what i found out

water into RO is 172, out of RO is 20 and out of DI is 4

So which one is broken?

Thx

here is a good read on ro unit maintenance

http://www.reefcentral.com/forums/sh...1415770&page=2

I don't think it works the way it looks like to you. I've never seen a phosban reactor, but am pretty sure most RODI system housings & tops are designed & built according to a generic standard. I think the water permeates the filter from around the outside (not the center) and exits through the core of the filter to the top. This would make sense particularly for the poly filters since the greatest surface area is the outside of the filter. It should be more efficient to push the water from the outer circumference to the smaller core. I can more or less confirm that since my 1 micron poly filter gets very gunky on the outside while the inner core is still fairly clean. Plus, it's unlikely companies would manufacture these generic/standard housings differently for a refillable DI or Carbon filter. Too easy to get things confused and mixed up.

I haven't taken a look recently, but if the refillable DI cartridge is built the same way as my refillable Carbon cartridge (which I took out a wile ago so I checked how it's built), then there will be slots around the bottom of the casing. Since the water can't permeate the sides of the plastic casing, it needs to enter these bottom slots and work its way up through the media then out the top center to the output. This should explain why there only needs to be a little water visible in the bottom of the housing. As long as the slots at the bottom of the refillable cartridge are covered, Bob's your uncle. There's likely sufficient air pressure in the outer housing to keep the water percolating up through the top of the DI casing and out. Again just thinking out loud and also trying to make sense of why this works without completely filling the DI housing. Would be nice if an expert from one of the RODI system sponsors could pipe in and provide clarification.

What type of RO membranes are you running? Most 75 gpd membranes will provide a rejection rate of at least 98%. If I've done the math correctly using your numbers I get a rejection rate of 88% and you're using two membranes. My single 75 gpd membrane takes the input TDS of 210 down to 1! I'd recommend having a look at your RO membranes. If their rating is more than 75 gpd, then the rejection rate will be lower, but with two membranes you probably should do better than 88% before the DI. You mentioned in an earlier post that you replaced the restrictor? Quite often the last component changed or disturbed in any system will be a good place to start looking for problems or errors.

Anyway i replied both membrane with 150GPD ones and also replace DI resin as well the flow restrictor and now it got 0ppm. However, one thing i found very interesting is that
after i replace the membrane, i got 4ppm come out and then go through a washout DI resin, i got 14 ppm. Is this normal or just weird?

Don't want to hijack the thread but don't feel like opening a new thread.
A question.
Do I need to add water conditioner(Prime) for the ro/di'ed water?

no you don't