pH issues...ARGHH!

[mini-reefer]

I have some questions on pH, alk and such(Please dont yell Broomer, Ive religiously read all your posts!).
It all started when I got my new Pinpoint pH monitor. I calibrated it with no problems. I stick it in the sump for the first time 11 days ago. It read 7.9! I USE TO rely on a Technika handheld digital meter. The only problem with it is the decimal only goes to tenths, not hundredths like the Pinpoint. So it could have been 8.10 or 8.19, but no way to tell. So anyways... I tested it against the calibration solution that I used on the Pinpoint and it read 7.4 in 7.0 fluid. Needless to say it was a bit off.
Now Im testing everything I can get my hands on. My Kalk mixed top off water pH is 12.7. My RO/DI fresh water is at 8.7 before mixing. Now where I start to get confused is after I mix the salt with it to the right specific gravity(1.023 at 79 degrees), the pH wont go over 7.9. Ive had 10 gallons mixing for a week and have been buffering it each day and it will go to 8.3 initially, but by the next day its back to 7.9. I dont want to use it for a water change and add to my pH issues in my tank.
Ive been buffering my tank about every other day and finally 11 days later with the lights out its at 8.17. By the end of yesterday when the halides went off it was at 8.29. I still have the dusty appearance on my live rock and coralline growth seems to be stunted right now. No corals SEEM to be affected. My fish appear to be doing well also.
Here are the results from water tests a few minutes ago:
Temp: 79.6
SG: 1.023
ph: 8.18 (actinics only)
Alk: 3.2
Ca: 300 (Im surprised at the Ca level. Usually its at 350(but wont go any higher, ever))
The only thing I think could be an issue is the RO/DI (4 stage) pre-filter. Its in need of replacement. But will this affect the final pH in newly mixed saltwater? I dont think so because the Instant Ocean salt should buffer the water to 8.3 anyway.
So what is happening chemically in my water? With the info given can someone give me a direction to head in? All input will be greatly appreciated.

 

[broomer5]

Mini-Reefer
Having two separate pH instruments - of different manufacturers - the chance of them ever reading exactly the same deminishes with the age of the electrode probe.
The fact that the Pinpoint reads to xx.xx the handheld Technika reads to xx.x doesn't help matters.
If you have done a 2-point calibration on the Pinpoint, otherwise known as a 2-point standardize and slope calibration AND it responded to the 2 different pH buffer solutions accurately - then you may consider the Pinpoint "calibrated" and accurate.
Sounds to me like the Technika probe is old and may need to be replaced. All glass pH probes wear out ( lose their electrolyte ) over time and eventually die.
The other fact that surprises me is that you measured your RO/DI water - and it reads 8.7 pH
Something is wrong with this picture.
RO/DI water should measure very near to 7.0 or even a little lower ( 6.8-6.9 )
Having an RO/DI freshwater source at 8.7 is odd - and would tell me one of two things.
Your RO membrane is damaged - and not doing it's job.
The mixed deionization resins ( cation/anion ) are old and no longer working.
What can happen on DI units - if the tapwater is excessivly higher or lower in hardness/minerals - either the cation or anion resin can become "depleted" before the other one get's depleted.
One is doing a grand job at pulling either the +ions out of the water, or is doing a great job pullint the -ions out of the water.
When this happens - it's time to replace the cartridge for sure.
In other words - only one of the DI resins is working right - it's removing either the positive ions OR it's removing the negative ions. Depending on which one it is.
Cation is working right - Anion isn't.
Or
Anion is working right - cation isn't.
This will tend to make the water more concentrated with pos or neg ions. Again - when and if this occurs - time for a new mixed DI resin cartridge.
What is the pH of your tap water ? If it's 8.7, and your RO/DI is also 8.7 ....... then the RO/DI unit is not working.
Lastly - CO2 gas definately affects the pH of saltwater.
CO2 gas in the room and CO2 gas in the saltwater itself.
If you don't believe this - half fill a glass with some fresh or saltwater.
Measure the pH - write it down.
Now place a straw in the glass and breath bubbles into the glass for a few minutes.
Measure the pH again.
It will most likely be much lower.
Your breathing exhaled CO2 into glass as bubbles - and this will increase the CO2 gas in solution.
Carbonic acid will form - and drive the pH down.
If your house is newer, and well sealed, and there are a lot of people/pets in the area - there is a chance ( slim but still a chance ) that this area is higher in CO2 gas.
Try setting a sample of saltwater outside, if it's not too cold in your area, and let it sit for a few hours.
Measure it's pH before and after sitting it outside.
See what happens ??
If you wanna try - up to you.
What else can you tell us about your conditions ?

 

[mini-reefer]

Well, before I say anything else about pH I need to double check my calibration on the Pinpoint. I know I got it right when I first did it. Tonight the meter is showing the low battery sign and it wont stay still while trying to recalibrate it. Its bouncing around A LOT. So tomorrow Ill grab a new battery while Im out and see if that helps settle it down.
As far as conditions go I assume you mean in the tank. The only thing I can think of I didnt mention before is the sand bed clumping up. My wrasse likes to dig around a bit and when he does you can see clumps of sand stuck together like layers, instead of individual grains. This does not appear to be all over, but just in a few places.
I did calibrate the Technika meterwith the 7.0 fluid and checked different water pH values. Granted I dont really trust it because of the variances from the Pinpoint, but here they are:
Fresh tap water: 8.5
RO/DI: 8.6(?)
Saltwater in a shot glass: 8.2
My RO/DI unit is only 9 months old so I assume the sediment filter needs replaced but the DI and RO membrane SHOULD still be OK. Underline should.
Anyone else have any experience with the Pinpoint monitor jumping around on the readings? Please throw in your input.
Please let me know any other thoughts or suggestions you might have before I can replace the battery on the Pinpoint Broomer. As always I value you input.

 

[broomer5]

If your sandbed is clumping - it may be a sign that the calcium and carbonates in the tankwater - precipitated out of solution and formed "calcium carbonate"
This may account for the clumping of sand. Think of calcium carbonate as the "cement" holding the grains of sand together.
If this did indeed happen - then it's very possible that your magnesium dropped considerably as well. This would also account for a drop in pH.
You can try to increase magnesium - although I always think that doing a series of water changes is a better approach.
Sort of get's things back into balance.
Yeah - get a new battery for sure.
The pH probe creates a millivolt signal.
The raw millivots generated by the pH electrode will normally read 0.0 to a -20 mV when placed into a pH buffer solution of 7.0
This is textbook for a new electrode.
As the electrode begins to lose it's electrolyte - the raw mV in a 7.0 buffer will tend to drift more towards the positive side.
If it reads +50mV in buffer 7.0 ~ it's normally time to replace the electrode.
Does your Pinpoint or Technika allow you to read the raw mV signal ?
In theory - most all glass pH probes work like this:
At pH of 7.0 = 0.0 mV
For every step change up the pH scale - expect a -59 mV change.
So at 8.0 pH the mV = -59
At 9.0 pH the mV = -118
And so on up the pH scale to 14 pH
At 14 pH the mV = -414
Going down the pH scale is the same incremental mV step changes.
At pH 6.0 the mV = +59
At pH 5.0 the mV = +118
An so on down the pH scale to 0 pH
At 0 pH the mV - +414
If your unit does not allow you to see the raw millivolt signal coming off the electrode - then your S.O.L. and must rely on your inability to calibrate it - to tell when the electrode needs replacing.
Your tap water and RO/DI water still is weird.
The pH of each is around 8.5/8.6
Again - something doesn't seem right to me there.
Try testing the alkalinity of the RO/DI water too.
It should be so low that the first drop of titration liquid you drop in will give you an instant color change.
This would be another good sign of something not working right with the RO/DI unit.
Also - check your waste to good water ratio.
If you're getting about the same amount of good water through the outlet, as you are the waste water - this is a sign too.
Maybe your membrane is blown a hole through it
Not sure - just another guess.
Lastly ~ is your tank or sump GROUNDED with a grounding probe ?

 

[mini-reefer]

Wow Broomer, do you ever run out of useful information? I think not!
Well the new battery worked wonders. The Pinpoint doesnt bounce at all now(note to self: dont use used batteries in a meter). I calibrated it again this evening and it seems to be very accurate. I put it back in the sump and its at 8.16 after the halides have been off. Ill keep an eye on it tomorrow and see what it says.
I also forgot to mention the additives I use. I also started to suspect a low magnesium level right after I got the meter and started doing more water tests. I started using Kents Tech-M. Ive dosed it twice in the last two weeks. Tonight I still see "clumping" in the sand bed. Before the Tech-M, I always have dosed Kent Essential Elements, Coral-Vite, and Iodine once a week since I started this tank. I also use Kents liquid calcium and Aragamilk daily. I REALLY started to notice coralline growth afetr starting to use the Aragamilk. Other than that I dont add anything to the tank exept Kent superbuffer DKH(a lot lately).
Is there something obvious Im missing? I wish there was a digital meter for every test imaginable for more accurate results.
Ill do more tests on my RO/DI unit tomorrow morning and post again. I hadnt thought of comparing the waste water with the "clean" water. It looks like I might be in the market for a new RO/DI unit soon because replacing all four filters would be just about as expensive. Ill also do the whole gamma of tests on the clean water and waste water to see where they are at in comparison to each other. Thanks for the suggestions Broomer. I just might get to the bottom of my problem yet.

 

[danrw84]

What do you keep your pH at broomer?

 

[broomer5]

Mini-Reefer
Glad to hear the Pinpoint is working better.
Good luck on the additional tests.
danrw84 - my tankwater pH swings like most folks.
I keep it above 8.0
I like it at 8.3
It moves around some on it's own - and this does not bother me, nor does it seem to bother the tank creatures.