DI section only works with little pressure?

[SF2K4]

So, I'm having a weird problem with my RO/DI set up. The TDS before the DI unit has been constant between 70-80. However, I can only get sub 10 (and rarely 0) after the DI section if I use very little water pressure. If I crank the faucet all the way open the TDS post-DI can get up to 40+. I've been told more pressure is key to getting lower TDS. What's the deal? I've only made around 50g of water.

[shifty51008]

something isn't right unless you have over 1000tds tap water.
check to make sure the membrane is seated fully in the chamber. what is the TDS of your tap water? wat is the water pressure comming into the RODI unit.

what unit is this?

[SF2K4]

Originally Posted by shifty51008

something isn't right unless you have over 1000tds tap water.
check to make sure the membrane is seated fully in the chamber. what is the TDS of your tap water? wat is the water pressure comming into the RODI unit.

what unit is this?

What should the TDS be like before the DI section (after the RO section)? Is 70ish too high?

I'll check the membrane. It's a Mighty Mite unit with a DI addition from Air, Water, Ice.

[shifty51008]

TDS on mine before the DI is 4. 70 is way to high and will use up your DI in no time.

[SF2K4]

I've gotten quite a few recommendations to check my tap's TDS. It's worth mentioning that I got this unit before I moved into my new apartment. However, I still live in the same complex. Never once had this problem at my other place. Is it possible that the building I'm in could have a vastly different TDS than the other?

[shifty51008]

it could but I highly doubt it, unless the plumbing is so bad from being old, but again I doubt it.

[SF2K4]

Surely it's not the filters then, right? I mean obviously they go bad eventually but not after only 50g or so.

[shifty51008]

no, the filters should be good

[d0ughb0y]

Originally Posted by SF2K4

What should the TDS be like before the DI section (after the RO section)? Is 70ish too high?

I'll check the membrane. It's a Mighty Mite unit with a DI addition from Air, Water, Ice.

if ro membrane rejection rate is 95%, then the tds after ro should be approximately 5% of the tap water tds.

[SF2K4]

So the TDS of my tap would be... 1400? That seems absurd... *** is going on?

[d0ughb0y]

can you measure your tap water TDS?
some ro membrane are rated 90% rejection rate, so your tap could be around 700. if ro membrane needs replacement, rejection rate will be quite lower than 90%. so you need to know what your tap water tds is.

[SF2K4]

My question is, even if the TDS in the source water was high, shouldn't it still work better at a higher pressure level? Or am I totally off base there?

[shifty51008]

RODI units work best at around 60-65psi. do you know what your pressure is at before the membrane?

[Uncle Salty 05]

It sounds like your membrane is not seated properly and water is by-passing it. Check to make sure the O rings are in good shape and seated where they should be.

[SF2K4]

These canisters aren't like the ones I usually see in RO/DI units. They don't sit below the unit but rather there's an inlet on one end and an outlet on the other... I'm not sure how to open them up... anyone familiar with the Mighty Mite?

[SF2K4]

Wasn't aware you were supposed to put the Mighty Mite as low as you can below the faucet to build pressure. Tried that, no such luck. However, no matter where the unit is or what the water pressure is, the TDS after the RO before the DI section is always right around 75. Does that mean the RO section is bad?

[Buckeye Hydro]

Originally Posted by shifty51008

RODI units work best at around 60-65psi. do you know what your pressure is at before the membrane?

I think what you meant to say was that popular brands of RO Membranes are factory spec'ed at 50 to 65 psi. They work best at much higher pressure.

Russ