Ro Water Ph Problems

[tomchurchman]

My new RO unit is producing water with a TDS reading of zero and the Ph is 4-5, pretty red, using the nutrafin wide band liquid. However, when I add minerals (Tropic Marin, tropical minerals - 1 and a bit spoonfuls, as stated) the Ph is jumping to about 7.6 (using nutrafin narrow band liquid test).
Any ideas whats wrong? these minerals should give a Ph of 7.
I've only just got the narrow band tester and last weekend was testing using the wideband and thought the Ph was around about 7, although its hard to be accurate.
If I leave the re-mineralised RO for a while, is the Ph likely to drop?

 

[tomchurchman]

tap water is around 7.2 - 7.4 Ph and a 50:50 mix of tap and un-mineralised RO is somewhere the same.
RO with minerals = Gh 120, Kh 60
RO w/o minerals and tap mixed 50:50 = Gh 120, Kh 60

 

[rabbut]

Mebe you should try adding a few less minerals. Watch the KH mind, if it falls below 2 german degrees of hardness (about 50ppm I think) the pH is likely to become unstable under normal conditions, and it needs to be above 3 if your injecting CO2

 

[OldMan47]

With what you are getting for a 50/50 mix, I would skip the artificial minerals and just use a 50/50 mix. It has a good pH, is quite soft without being dangerously so and should be appreciated by most community fish. You haven't said what your target conditions are but I would keep almost anything that is freshwater in your 50/50 mix without batting an eye.

 

[Colin_T]

you could have a dodgy test kit. R/O water should come out at close to 7.0 not 4-5.
Maybe take a sample to the lFS and have them check it.

 

[tomchurchman]

Thanks for the replies. I'll get the RO checked, but my wide range test kit seems pretty good when testing the aquariums, definately orangey red when testing RO though.
As for conditions, I'm aiming for a Ph of just below 7, with fairly soft water. Looking to keep some South American species such as Corys, Hatchetfish, Tetras (haven't decided which yet) and a couple of Chichlids (dwarf cockatoo possibly)

 

[Bignose]

you could have a dodgy test kit. R/O water should come out at close to 7.0 not 4-5.
Maybe take a sample to the lFS and have them check it.

Colin,

Theoretically RO water does have a pH of 7.0-ish (the hundredths and thousandths decimal place depend on the temperature), but in practice because RO water is so devoid of anything, the smallest amounts of any additive/impurity in it can make the pH swing several units. That is, a little dissolved CO2 from the air can push RO water to read in the 4's, or of a drop of two of mineralized, hard, high-pH water accidentally gets mixed in (like if you didn't clean out your test tube, for instance), then the pH can be up in the 9's or 10's. RO's water pH is highly unstable and it seems everybody who tests gets different answers.

Nevertheless, having your LFS test the water for you is almost always a good idea. Having a second test done should increase the confidence you get in the number.