RODI water problems

[maelstroem]

Hi

I have recently purchased a 6 stage reverse osmosis system as follows.

1.Sedement Filter. 2. Pre Carbon Filter. 3. 2nd Carbon Filter. 4. 100gpd Membrane. 5. Post Filter De-ionisation cartridge. 6. Post Filter Carbon cartridge.

 

It is all set up in a brick outbuilding - water pressure exactly as required by the manufacturer.

The water is being collected in food grade  25 litre tubs that have been thoroughly washed out with clean water.

 

The manufacturer stated that the unit needed to be run initially disposing of the first 25 litres to remove the food grade preservative in the membrane - i decided to

dispose of the first 50 litres to be sure.

 

The mains water entering the unit is PH 8.2 TDS 370.

 

After collecting the first 25 litres of RO Water it tested out as follows:- TDS 10 PH 9.8 KH 0 GH 1. ( using hand held meters for TDS and PH and using API drops for GH and KH. )

 

I was confused with the PH reading being 9.8 as I was expecting it to be well below 7 ( nearer 6 ).

I looked online and found that a number of people saying that trying to check new RO Water for PH was almost impossible due it's lack of composition.

 

So I treated 25 litres of RO Water with Salty SHrimp GH+. After thoroughly stirring for a while I re-tested the water with the following results:-

TDS 110 - GH 2 - KH 2.5 --- BUT the PH is still in the high 9's - I did another check with API drops PH test kit and it was showing the same result.

 

Can anyone tell me if I am missing something out or explain why my PH is not in the 5's or 6's.

 

Thx M

[madcrafted]

In order to see where your pH settles when it reached equilibrium with atmosphere, you will need to aerate your water first. This will give you your nominal pH value. Being as r/o water has no influence by bi/carbonates, it's pH will be unstable right from the unit. Having said that, it is unusual to see such a high reading. Mine is usually around 6.8 -7 in my holding tank but it drops about a whole point after I place r/o water in sealed jugs (due to formation of carbonic acid). I don't aerate my water either because I need it to be low for water changes and top offs for the species of shrimp I keep. Your pH will never reach below 7 if using some sort of re-mineralizer with KH+ and no buffering substrate. I assume you are keeping neos, so a neutral pH is desired. Again, you should still try to add an airstone to your holding water first, just to see where it brings your pH before adding your re-mineralizer so you can have a reference to where your r/o water settles without the influence of bi/carbonates (KH).

[hcuellart]

The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit's indicator dye is enough to alter pure water's measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

 

Found the above on a reefer forum, they also suggested aerating the water for a while...

 

[MNCarpenter]

Where is the 2.5 kh coming from? Are you using a gh/,kh remineralizer? You said it was just GH+ but id double check the container if your not keeping neos.

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[maelstroem]

Hi again

 

Thank you for your replies.

 

I am preparing a tank to keep caridina cantonensis 'Golden bee'.

I am trying to get my water to Kh 1 - Gh 3 - tds 150 - ph 6.3ish.

 

I have only remineralised with GH+ - i haven't used the GH/KH+ version.

 

I will now give the water a few hours good aeration and see how we go.

 

Again thanks for the info - much appreciated.

 

M

[madcrafted]

1 hour ago, maelstroem said:

 

 

I have only remineralised with GH+ - i haven't used the GH/KH+ version.

 

 

Oh. This changes everything. I assumed since the KH value went up, you were using a re-mineralizer with KH+. If it's not the added minerals, then something is leeching carbonates into the water. Are you getting your final results (KH= 2.5) after it's added to the tank? If so, what substrate are you using? Are there stones in this tank?

[maelstroem]

Hi

 

I have just redone all the previous again - the rodi water still in the tub added the gh+ the same as before and run all the tests as before and it seems there may have been a bit of something in the tubs i wasn't aware of as the KH has now remained at zero, however the PH is still registering in the high 9's after an hour of aeration , so I am still wondering how I am going to get consistant PH water in the low 6's. Everything else seems to be performing as expected KH=0 GH=2 tds=(6) immediatly after production rising to 140 after adding the GH+.

[hcuellart]

You need to test again after 24 hours of aerating the water to have a better idea. Is your pH testing pen calibrated correctly? 

[maelstroem]

I did a calibration to 4.0 and 7.0 just to make sure, with the same results.

But I will test again after 24 hours aeration and see what we get.

 

Again thx for the help.

 

M

[MNCarpenter]

So sense starting shrimp iv quit using a ph pen. If the Kh is 0 your active substrate will drop it. You could try putting a nylon filled with a cup of substrate of your choice and hang that in your wster while you aerate it. But with no kh the ph pen will not work well. I spent a good bit of $ and it still would take the ph meter 10 minutes to get close to the ph i thought it was supposed to be. But once you get your system down ph is the least important test. Gh +tds are the big ones.

 

One other thing you coukd do is run co2 through your water for a bit. Either from a tank or even a yeast n sugar bottle would work

 

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[maelstroem]

Thank you for all your help - will try this.