RO/DI Help

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Sliced Bread
Dec 25, 2006
Northern Virginia
Alright, I'm quite frustrated here.

I have an RO/DI unit, purchased from ebay, 6 stage, 100gpd. It's a few months old, but I've probably only put 200 gallons through it so far. Now that my tank is actually going up, I'm really starting to use it, for obvious reasons. The thing is slow as dirt. I've seen paint dry faster. What can I do to help it out.

I don't know my water pressure, I'm looking for a gauge to measure it. I expect to find it's in the low range. And of course, this time of year, the water temp on the inlet is low, mines at 45 deg F.

I'd guess that I'm only producing about 20gpd right now, and that's just not acceptable.

My waste water line has a nice, constant decent stream of water, and out of the pure water line I get drops, about 5 per second.

any suggestions? It's going to take a week to fill my tank at this rate.
I'm sure you have, but have you adjusted the flow rate up and run a TDS test? I know u posted b4 but what is source source TDS?
Not sure what you mean by adjusting the flow rate up, can you elaborate?

In the summer my input TDS ran in the low to mid 200s. Right now, it's in the low 100s usually, it's reading 95 right now. Output is at 0.
no, water pressure is at whatever is normal for this place. I'm tapping the unit right where the water comes into the utility room from underground.

It didn't run any better than this (or at least not much) in the summer.
Mine has an adjustment on it where I can increase or decrease the waste flow. What I did was start it high (less waste , more 'pure') then test the TDS. I adjusted the flow to more waste/less pure until I got a 0 reading. I check it monthly and adjust it as I need to. After a few months I back flush the whole thing and start again.

If you want I can post up a schematic of mine and you can compare

BTW: my water pressure is 57 and TDS is 260 out of the tap.
Here is a link to my instructions. I have the aquarium model that has 3 DI cans on it. I only run one at a time and still get 0 TDS

Alright, I don't have that valve. Mine just has a big, long barrel, about 6" long and 1" OD, no adjustment on it at all.

I'm running an experiment right now. I saw this idea on melev's reef. I took a bucket of hot water and 25' of tubing, and routed my source water through this coiled up 25' of tubing in hot water to see if it will raise the temperature of the water that's hitting the membrane and produce better output. The unit holds probably 1.5-2.5g of water within all the filters, so it'll take a little while to get it all warmed up, but just feeling the water lines I can tell that the intake water is really cold, and it's nearly room temperature after going through the bucket of hot water.

Think I'm going to start looking for a booster pump. I know sells them.
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The value just allows you to control the pressure/thru put on the membrane. The other option to try (before the booster) is to but a cheap tap adapter and try warmer water.

Another dumb question; but you're sure your connections, membranes etc are all seated correctly and not obstructed?
Mine always runs slow in the winter. The cold water is the reason it runs slow. I can fill up a 5 gallon jug in the summer in about 3-4 hours but in the winter it takes 7-8 hours. I run the coralife maxima.
well my warm water experiment yielded no blatently obvious results. Next step is to check the pressure, then boost it. I suspect this is the culprit.
Neilan and I were talking about this the other day. I have a similar unit and I am able to fill my 32g trashcan in less then 12 hours. I'm on well water here and I'm getting about 55psi at the tap.

I'm wondering if maybe there is a filter that isn't seated or has something blocking it. I can't imagine city water being short on pressure espeically in the area you are in. That is a somewhat recent development. Less then 10 years old I believe.
So finally got a pressure guage. Couldn't find one locally (believe it or not) so I ordered an inline one from AWI and it just got here. I tapped it in between the piercing saddle valve where I tap my water supply and the input to the filter. I'm getting 48psi. Maybe a little on the low side, but not enough I would think to give me the results I'm seeing.

The other night I did some more investigating. I disconnected the input to the RO membrane and checked the water flow through the first 3 stages since this was simple enough to do. Have plenty of pressure there. Then, the output of the membrane is at a trickle, so the issue is in there somewhere. Either it's not seated right, or it's a bad membrane is what I'm thinking.
The home RO membranes are designed for 60 - 100 psi. If your tap doesn't have that, then a booster is in order. Additionally, the performance increases with the higher pressure (TDS output is lower if input pressure is higher). If you have a lot of bio's in your water, it will speed up the decay of the membrane too.
The home RO membranes are designed for 60 - 100 psi. If your tap doesn't have that, then a booster is in order. Additionally, the performance increases with the higher pressure (TDS output is lower if input pressure is higher). If you have a lot of bio's in your water, it will speed up the decay of the membrane too.

I think there is more to it then the pressure. I am on a well and have a pressure tank to feed the house we are set at 55psi in the house and my RO/DI unit will fill a 32g trash can in less then 12 hours.

Most RO/DI units sold should be anywhere from 50-70psi. With water temps in teh 70s they will produce at max performance. My water out of the tap is 57.3 and I'm still generating that amount of water with 0 TDS output.

I think Neilan is correct in that there is something wrong with his membrane.
We have a brand new (about 1 mo old) 6 stage unit. It is filtering at a trickle in this cold weather as well. Cold here has meant sub zero. We have a 35 gallon garbage can that the filter runs into. We turn it on in the evening and let it run all night. That seems to work ok (except for the day that I went to school and forgot to shut it off!). Weather is definitely a factor. I just filter constantly. 35 gallon garbage can and lots of 5 gallon buckets!

Remember: cold is a relative descriptor depending on where you llive!
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just an update. I had finally gotten convinced something was wrong, more than just pressure and temperature, so I bought a replacement membrane.

My production is up more than 300%.
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