Ro water question

[Maridia]

I recently replaced the filters on my ro unit. I did a few flushes over a 3 day period and just now tested for tds. I get zero for both GH and KH. But here's the funny part, my ph is at 8.0. Is the water so pure that the test can't read it? Before swapping ro filters, my ph was 6.5. I thought this number was more typical. I'm using an ati liquid test kit. Any info would be great. Thanks!

 

[J.Mcpeak]

It depends when/how you tested the water. You get equilibrium across the membrane after shut off, but only if it is left pressurised. Those first few minutes at re-start will be equalised, the TDS will be higher at the membrane output NOT the waste water (The output jumps up to input level briefly)
Normally RO water settles at pH 4.5-6 (mine does anyway)

Without gh (to a point) Kh (mainly) or biological activity the water normally acidifies, this is due to the Co2 in the atmosphere.

The accuracy of the test itself also needs to be considered, take a decent sample and clean the test equipment with half of the sample water, then tests can be carried out on the other half of the sample.
(Develop OCD, clean three times <I did! )

Do not contaminate the sample.
hope this helps.

 

[Maridia]

It's been running for about 4 days. I've even drained the tank twice a day since then. Yes, my tds were zero for both kh and gh. But the ph was 8.0. Yes I rinse the test tubes with ro water. Do not use my thumb to test.

 

[J.Mcpeak]

It's possible the filters were not changed in time, the chlorine that makes it to the RO membrane will damage it in no time at all. Just a sniff is all it takes.

Measure TDS before and after RO membrane.

FORMULA= (TDS Input - TDS output)/output X 100.

Eg,
(tap water reads 450ppm TDS, and Reverse Osmosis filtered water reads 15ppm.
450-15=435
435/450=.966
.966*100=96.6%
So, my reverse osmosis is running at 96.6% TDS reduction.)

That will tell you if your membrane is kapoot. Three days is far too long!

I installed a meter to check, if you use a lot of water I would suggest one. I use the RO-man system and I get through the 3000 gal CCB in 8-10 weeks, that's miles away from six months! I upgraded to longer life high capacity filters, this comes with problems though, so I don't recommend it unless you know what you are doing. They should last me 12 months, or near enough. It's my first time with them, they are only 1 month old, we shall see?

A full account can be found on my flickr profile, sets, my fish house, it's the last few pictures within that set. (the ones with RO units in them!) a shorter version is available in my fish house link.

 

[Maridia]

It's possible the filters were not changed in time, the chlorine that makes it to the RO membrane will damage it in no time at all. Just a sniff is all it takes.

Measure TDS before and after RO membrane.

FORMULA= (TDS Input - TDS output)/output X 100.

Eg,
(tap water reads 450ppm TDS, and Reverse Osmosis filtered water reads 15ppm.
450-15=435
435/450=.966
.966*100=96.6%
So, my reverse osmosis is running at 96.6% TDS reduction.)

That will tell you if your membrane is kapoot. Three days is far too long!

I installed a meter to check, if you use a lot of water I would suggest one. I use the RO-man system and I get through the 3000 gal CCB in 8-10 weeks, that's miles away from six months! I upgraded to longer life high capacity filters, this comes with problems though, so I don't recommend it unless you know what you are doing. They should last me 12 months, or near enough. It's my first time with them, they are only 1 month old, we shall see?

A full account can be found on my flickr profile, sets, my fish house, it's the last few pictures within that set. (the ones with RO units in them!) a shorter version is available in my fish house link.

I measured my tds, all zero. So it doesn't make sense that I would have a ph of 8.0. I think I recall this happening before... After some time, a week or 2, ph started measuring 6.5. Is it possible for your water to be so pure that a ph test can't really read it, thus giving you bizarro numbers? Just a thought.

 

[J.Mcpeak]

No it is not possible, not by my experience. No bizzaro, no way. Not for as long as I've had RO.
Your pH test will give a reading, if it's the lowest possible (6.5 for API) it may well be below that.

All TDS readings of zero means your TDS meter is, being incorrectly used, broken, incorrectly calibrated or the batteries need replacing.

You should have a reading close to your tap water after the prefilters.
After the membrane the reading should be as close to zero as possible but is never zero. (After the equilibrium spike I mentioned before has been allowed to dissipate)

After the DI stage you will get zero but not forever.

Edit-
When you flushed the filters, did the water make it to the membrane?

The CCB should be disconnected from the membrane and the flush cycle should be allowed to drain elsewhere. I'm sure the carbon fines can damage the membrane. Once the filter is flushed this is no longer a problem.
The carbon fines are remains of the manufacturing process.

From the start (all new filters)
Add micron filter and CCB, disconnect pipe to membrane input, this pipe goes to waste.
Flush pre filters. (25 litres I think does it)
Connect pipe to membrane, disconnect DI resin bed, begin flush cycle on membrane, discard first hour of permeate. Connect to DI resin bed, begin production.
(Assuming 60psi and 24'C feed temp)

DI resin does not need rinsing.
If you have a heavy metal resin stage this needs to be flushed.

Who makes your unit? Model number etc. does it have a pressure gauge?

 

[J.Mcpeak]

It's been running for about 4 days. I've even drained the tank twice a day since then. Yes, my tds were zero for both kh and gh. But the ph was 8.0. Yes I rinse the test tubes with ro water. Do not use my thumb to test.

Your reading for GH is 0mg/l
Your reading for KH is 0mg/l
I realise this easily converts to TDS ppm.

You may still have a reading of TDS.
A TDS meter will allow you to read increments of 1ppm TDS.
This will be all GH/Kh and a whole bunch of other things not a specific test but a broad test of your total dissolved solids.

 

[Maridia]

Your reading for GH is 0mg/l
Your reading for KH is 0mg/l
I realise this easily converts to TDS ppm.

You may still have a reading of TDS.
A TDS meter will allow you to read increments of 1ppm TDS.
This will be all GH/Kh and a whole bunch of other things not a specific test but a broad test of your total dissolved solids.

ah yes. I may have gotten confused with the details. My GH and KH read 0mg using the API liquid test kit. I assumed it was the same as TDS. So you're saying there may still be some TDS in my water, causing ph to be 8.0?

 

[J.Mcpeak]

Er. . . The only thing I can think of, perhaps you've crossed over the output pipes. (It seems wrong though because,)

The production water if passed through DI is neutral for a small time then it acidifies. No Kh is the reason.

You have no Kh, No GH. Crossed pipes is unlikely with these results.

Is the test kit up to date? This should not be happening.

I tested my production water,
it is TDS 004,
ph 5,
GH/Kh 1. (Up to 17.8 mg/l each for GH and Kh.)
1dH = 17.8 mg/l that doesn't result in pH 8.

Consider the pH kit is past useful life?
Invest in a TDS meter.

Which pH test(s) do you use? (Ranges)
At this point I use the JBL wide range 3-10 (covers RO and my buffer mixes)
and the API ranges (high/low) 6.5-7.6 & 7.4-9 I think it is, for tank duties. The API kits cover the ranges most life and available fish need to survive in.

I find the jbl kit hard to read between 7ish and 8ish, every time is just a guess in these ranges, when compared to the API my guess is always wrong, the API kit is cheap enough and precise enough for an idea. Normally they work, quick and easy.

 

[Maridia]

Er. . . The only thing I can think of, perhaps you've crossed over the output pipes. (It seems wrong though because,)

The production water if passed through DI is neutral for a small time then it acidifies. No Kh is the reason.

You have no Kh, No GH. Crossed pipes is unlikely with these results.

Is the test kit up to date? This should not be happening.

I tested my production water,
it is TDS 004,
ph 5,
GH/Kh 1. (Up to 17.8 mg/l each for GH and Kh.)
1dH = 17.8 mg/l that doesn't result in pH 8.

Consider the pH kit is past useful life?
Invest in a TDS meter.

Which pH test(s) do you use? (Ranges)
At this point I use the JBL wide range 3-10 (covers RO and my buffer mixes)
and the API ranges (high/low) 6.5-7.6 & 7.4-9 I think it is, for tank duties. The API kits cover the ranges most life and available fish need to survive in.

I find the jbl kit hard to read between 7ish and 8ish, every time is just a guess in these ranges, when compared to the API my guess is always wrong, the API kit is cheap enough and precise enough for an idea. Normally they work, quick and easy.

Last night I filled 2 gallons of ro and I got the same results, gh zero, kh zero. I just added 1 drop of the test, and it's already the correct color. Ph was still 8.0. I added API powdered proper ph 7.0, 2 hours later, I tested again, boom! My ph was actually 6.6-6.8. All my tests are still up to date. It looks like history is repeating itself again. It was like this the first few weeks, so I added proper ph and used the water for top off. About 3 or so weeks later, tested ph again, 6.5. Quite a mysterious situation... I'm not really worried about it, I just wanted to see if anyone ever had a similar experience. Thanks to all.