HIGH PH from RODI

[DzidtheReefer]

Ive read many posts from fellow reefers and Randy himself that I shouldn't worry about my water PH being high coming from the RODI unit. But I want to see if I can specifically get an answer to my problem

The water that is made from my RODI unit is 8.8-8.7. I usually make 30gals at a time, it reads 0 tds. I change out my filters and membrane every 3 months which some might say is an overkill but ill take peace of mind anytime. Now when I mix the water with Fritz salt to 1.026 salinity, alk is 8.0-8.5 depending on the batch, but my PH than reads 8.6 to 8.7.

Now 24hours later, I add this water to my tank, which is a mixed LPS/SPS/Softie tank that I dos with BRS calcium, alk, and magnesium. I have this controlled over my apex, and my PH CONSISTENTLY in my reef tank is 8.67-8.77 within a 24hour period. When I have my refuge light it drops down to 8.67, during the brightest time of the day my PH is 8.77. ALK is consistent 8.4, calcium 440, and magnesium I barely measure but I don't think these have anything to do with PH levels, besides alk. Nitrates range from 10-20ppm, and phosphate according to hanna is .02-.03 if anyone is wondering.

My question is, ive been able to keep my PH pretty consistent, should I even worry about lowering my PH? Ive dosed vinegar before,30mls a day, which is nothing for 150gals of water volume, only to bring PH down, but only to see it go up again an hour or two later. What other solutions are there so I can lower my PH from my rodi unit so I can overall lower my PH in my reef tank to 8.0.

 

[Dkeller_nc]

It's extremely unlikely that your pH is actually 8.6 - 8.8 in your tank. That's because the equilibrium pH with our current atmosphere (ca. 400 ppm CO2) of seawater at 1.026 specific gravity and roughly 25 deg C is about 8.3.

There are several possibilities that would explain the discrepancy; the first is the most obvious, which is a miscalibrated and/or failing pH electrode. That miscalibration can be from user error, but is probably more likely due to old or flat-out incorrect pH calibration solutions.

Another possibility is a considerably more concentrated seawater solution than 1.026 specific gravity. Similar to the pH probe, this can be the result of a miscalibrated or malfunctioning refractometer and/or conductivity meter.

With respect to your RODI water, the pH is irrelevant because if it's correctly produced at TDS of 0, it has virtually no buffering capacity. And because it has no buffering capacity, it's not possible for it to have any measurable effect on seawater produced from it.

 

[DzidtheReefer]

Thank you for your reply.

I don't no if i can agree since ive taken all steps to make sure it is not user error. I purchased a new PH electrode, recalibrated it, and get the same value. On top of monitoring it with my electrode, I also measure my PH with API kits and a hanna PH tool and keep getting the same value of 8.7 roughly, depending of time of the day.

My previous electrode is only 4 months old. I measure the salinity of my water with a refractometer, and just recently started using a Milwaukee refractometer and get a consistent salinity of 1.026. When I make saltwater, I weigh out my salt, and add portions at a time so i don't get spikes of any level. All my corals and fish are fat and healthy, and I haven't suffered a fish loss since I set this big tank up from the very beginning.

But is there anything I can use to decrease my PH from my rodi unit? Using limewater for example? Should I even worry about decreasing my PH if all livestock is doing well?

 

[Randy Holmes-Farley]

pH meters are incapable of measuring the pH of totally pure water. It’s not user error. It is method failure.

Mine read high in pH too. I don’t know why or what exactly it means, but it is zero concern.

 

[Randy Holmes-Farley]

Limewater would raise the pH to 12+.

As an aside, if you take totally pure di water with a pH by definition of 7, and mix it with seawater at pH 8.1, the final pH will be higher than 8.1. There’s a reef chemistry question of the day explaining exactly why, but unless you are into chemistry, the take home message is pH is more complex than reefers assume.

 

[Randy Holmes-Farley]

I should note that an imbalanced di can give high or low pH and not 0 ppm tds. There can be residual HCl or NaOH in the water.

 

[JoshH]

On a side note and unrelated to your question but, RO Membranes should last you years, no need to be replacing those every few months, your literally just throwing money away And Resin only needs to be replaced when your output starts getting above Zero. I do like the replacment Sediment and carbon every 6 orso months, until you know exactly how much water your making then you can just replace it based off of the lower end of the capacity of the filter. Probably get you a few more months use even doing that

 

[DzidtheReefer]

Thank you for your responses. So I should not worry that my PH is hovering around 8.7ish with all the tests that I perform. And I changed out the membrane just because I thought for whatever reason that was the cause of my PH being high to begin with. I just wanted to make sure I covered all the variables before I posted a thread

 

[Randy Holmes-Farley]

Thank you for your responses. So I should not worry that my PH is hovering around 8.7ish with all the tests that I perform. And I changed out the membrane just because I thought for whatever reason that was the cause of my PH being high to begin with. I just wanted to make sure I covered all the variables before I posted a thread

Correct. Tds is the only useful test for ro/di.

 

[Dkeller_nc]

Thank you for your responses. So I should not worry that my PH is hovering around 8.7ish with all the tests that I perform. And I changed out the membrane just because I thought for whatever reason that was the cause of my PH being high to begin with. I just wanted to make sure I covered all the variables before I posted a thread

You shouldn't worry about the RODI water presuming that your TDS is actually zero. And as Randy notes, it's not possible to accurately measure pH in highly purified water with a pH meter.

However, there's definitely something odd about seawater at pH 8.7.

 

[DzidtheReefer]

Ive been running high PH for about 6 months now in this new tank. i set up a dos last night, dosing alk at night and calcium during the day. im trying to stablize my swings