pH too high: 8.65. Won't come down.

[litvin.gridneff]

pH is 8.65. I can't get it down.

The pH in my 180 gal tank has been climbing up for a few months. It is now approaching 8.7 and my softies are starting to look stressed.

The pH probe is fine. It's less than a year old. I have just cleaned and recalibrated it. The freshly mixed batch of Kent salt water reads at 8.36. My tank reads at 8.65.

I do not dose kalk or a 2 part ca/alk either. I do run the calcium reactor.

I tried dozing vinegar following the advice found in http://reefkeeping.com/issues/2005-03/rhf/index.htm. Adding the recommended 1 ml/gal to the tank does bring pH down from 8.6 to 8.3 as expected. However, the pH climbs back up within 24 hours.

I had to stop playing the vinegar rollercoaster after 3 days because my green bubble started to look miserable. To my horror, the dKH climbed from 11 before the dosing to 15 and continued climbing to 20. To rule out the wonky Alk test, I tested the freshly mixed batch. It reads 8.3 dKH.

I just did a 20% water change. The pH is down 8.56 and Alk is 15 dKH. I shut off the calcium reactor and am monitoring the situation.

I am still at a loss what is pushing the pH and Alk up so much.

Water chemistry:
Salinity 1.024
Temp 77-78
pH 8.65
Calcium 480-500
Mg 1320
Alk normally in 10-12 dKH range.
NO3 normally 0.25-0.5 range. Vinegar dosing reduced it to 0 as expected
PO4 0.1-0.2 range.

I run a Diablo skimmer and some cheto in the sump. I ran the fuge lights 24h but went to reverse 8pm-8am cycle a few days ago.

Theories anyone?

 

[bertoni]

That pH level sounds like a measurement error. Since you've cleaned and calibrated the probe, my first guess would be electrical interference of some sort. I might try measuring a cup of tank water well away from the system.

Kalk is about the only way to drive the pH to that level. Given that the tank has a skimmer, and the alkalinity is in the normal range, I don't think the pH is likely to be that high. I might check for signs of a surface film, but that'd cause a lower pH at night.

 

[litvin.gridneff]

I shut off the CO2 to the Calc reactor and increased the flow rate. The pH probe in the reactor reads 8.63. The probe in the tank reads 8.68.

The tank is grounded. To rule out the electrical interference, I put the probe in a plastic cup and let it sit for 20 minutes 3 feet away from the tank. The pH read 8.66.

I think we can safely rule out a miscalibrated probe or electrical interference.

I remeasured the calcium and Alk. The calcium shot up to 540 from 480 a week ago. The Alk is down a bit more 14.2 dKH.

But pH remains stubbornly high.

 

[litvin.gridneff]

I should mention I am also running Brightwell's Neomag in my calcium reactor and. I just dug out this blurb from http://brightwellaquatics.com/products/neomagt.php.

"Regardless of the method utilized, it is not recommended that the ratio of aragonite:NēoMag exceed 7:1 by volume, as this may increase the alkalinity of the aquarium beyond the desired level." I think my ratio is more like 5:1 since I could never get it dissolved at 6.5 pH.

As an experiment, I am completely shutting off the reactor for a week to see what happens to pH.

 

[Optionman]

invite a bunch of people into the room with the tank (have a party) and let the CO2 produced drive the tank PH down. just a thought

 

[CrayolaViolence]

Wouldn't soda water bring down the ph?

 

[bertoni]

So nothing is going into the tank at this point? Is this tank in a house? If so, I expect better aeration should bring down the pH. I might try aerating a cup of water next to the tank for 3 hours, and then measure it.

Soda water will bring down the pH temporarily, like vinegar, but it won't add organics, so it's a bit safer to use. I should have mentioned that. Thanks for reminding me, Crayola.

 

[litvin.gridneff]

I might try soda water or even hydrochloric acid. See http://reefkeeping.com/issues/2005-03/rhf/index.htm

But not until Alk drops to below 11.

 

[bertoni]

Hydrochloric acid might drop the pH too much, and it will consume alkalinity from the water column. I wouldn't use it on a running system.

 

[tmz]

Selzer is safer, IMO. Vinegar adds organic carbon; hydrocloric acid is to strong for fro a living system In the article cited by Randy Farely he notes 6ml of seltxer water per gallon of sytem water will drop pH by 0.03,FYI. Alternatively you might try just bubbling in a small amount of CO2 directly without going through the media in the reactor ,since you have the equipment . Once you get the alk and pH down , you can dial the reactor back in at a lower dosing level by reducing the CO2 injection rate