High Alk, low pH

[pseudorand]

My tank just tested at a pH of 7.4 and dKH of 10.4.

Fortunately this is my QT tank. It's been empty for a few weeks and I'm getting it ready for new fish. I just did an 80% water change to drop Cu. Since there's nothing non-microscopic alive in it, I dumped in ~65F water at about 1.020 specific gravity and dumped more salt (Red Sea blue bucket) directly in the tank to bring it to 1.025. I suspect it's related to having just mixed the salt, but it had been mixing for a few hours before the water test and it's up to 78F, so I thought it would have stabilized by now.

I've never seen pH that low in saltwater before. What's going on?

Is this a problem for a fish-only QT?

Should I expect the pH to come up to ~8 or so by morning?

Did I kill all my bacteria / do I have to re-cycle the tank now?

 

[Dr. Dendrostein]

My tank just tested at a pH of 7.4 and dKH of 10.4.

Fortunately this is my QT tank. It's been empty for a few weeks and I'm getting it ready for new fish. I just did an 80% water change to drop Cu. Since there's nothing non-microscopic alive in it, I dumped in ~65F water at about 1.020 specific gravity and dumped more salt (Red Sea blue bucket) directly in the tank to bring it to 1.025. I suspect it's related to having just mixed the salt, but it had been mixing for a few hours before the water test and it's up to 78F, so I thought it would have stabilized by now.

I've never seen pH that low in saltwater before. What's going on?

Is this a problem for a fish-only QT?

Should I expect the pH to come up to ~8 or so by morning?

Did I kill all my bacteria / do I have to re-cycle the tank now?

If my tank, add small reactor with argonite sand, gentle tumble, why argonite? It starts desolving at 7.8, ands other elements when desolving and stabilizes ph. Get test kits to have better picture of water perimeters. Since you did provide complete info of water perimeters. We're thinking your missing emergency kit. Seachem basic kit a must. My thinking.
Forgot to mention your alkilinity high, let it lower by its self. I had last month a dosing pump fail and dump 3/4 of a gallon of soda ash into 120 gallon volume. Alk was 16 took 3 weeks to stabilize, no stress or loss of corals.


Picture of dendronephthya umbellulifera one of the rarest and difficult to raise in reef tanks. 1 of 15.

 

[Memisis]

Does your freshly mixed salt water measure to expected alk? I recently drove a tanks alk way down because the API titration test i was using was consistently giving me a whole 4 dkh lower than what it was. I started having issues with corals and got a hanna to find it was super low (low 7's). My ph swings from 8.15 to 7.85. It was as low as 7.65 when the alk was low. I think I was on verge of a crash.

I agree that the dkh of 10 and low reading may not add up. Check your test kit.

The other possibility is Co2 driving your ph down. Do the bring tank water outside and aerate for a few hours test to see if it goes up dramatically. If so you need to feed your skimmer fresh outdoor air to solve ph issues.

Best of luck and keep us updated.

 

[josephxsxn]

I agree with others it sounds like co2 driving your PH down. Here is a image that they use with planted tanks that shows where your PH will be based on current DKH and Co2. Now a days because I keep my DKH pegged at 7.5 I can walk by a PH monitor and know if my skimmer is not running because the PH will drop due to reduced gas exchange.

PS - I ran the skimmer line outside on my display.

 

[pseudorand]

I'm pretty sure it's not co2.

It could be in my mixing bucket because it is covered. I have a powerhead in it, but it doesn't cause much surface agitation.

However, the QT had two powerheads and a bubbler in it for a few hours before I tested, so plenty of surface agitation there.

I do have precipitation in my mixing bucket. Anyone know if that can drop pH? Or what to do about it?

 

[josephxsxn]

I'm pretty sure it's not co2.

However, the QT had two powerheads and a bubbler in it for a few hours before I tested, so plenty of surface agitation there.

If the air inside (source) has a higher concentration then it would eventually bring the tank to that balance unless you using co2 removing media or bringing in air from an outside source. If your sure your DKH level then the only other input to get PH is the co2 levels in the tank (you can go in reverse with the chart using DKH and PH). I could never get my tanks over 7.9 PH highs with indoor air, but outdoor air has significantly less co2 and when ran through the skimmer the tank slowly moved into equilibrium with that source raising me to 8.1 lows and higher during daylight period. Of course in our displays the daylight period raises our PH because the alages are consuming co2 as well.

The basic test is to take a cup of water and a airstone outside for a a few hours and test if the PH went up or not. If it does then your problem would be co2 or gas exchange. If you have sufficient gas exchange then the source is likly high in co2. Pretty much all modern homes have higher levels of co2 then outside. This is why some people can open a window and increase the PH of thier tanks.

Of course covering things could reduce gas exchange too just like your thinking with the lid.


Edit - thought it good to link Randy's article http://www.reefkeeping.com/issues/2004-09/rhf/

 

[pseudorand]

Well, this morning the tank pH is at 8.0+ and my fresh salt mix is about the same, possibly slightly lower. I guess that's why we don't mix in the tank if there are living things in it.

I'm surprised it took more than 2 hours to stabilize though, since red sea instructions say not to mix more than 4 hours.