My pH dropped....

[LynnCeeBee]

I've been testing my water weekly, so this happened within the last week. Normally, my tests show no ammonia or nitrite, my nitrates around 15, and my pH around 8.2. Last week, I upgraded my RO to an RO/DI unit, and have been using that for topoffs and my PWCs. This evening when I tested, my nitrates had dropped to below 5 (hurrah! hurrah!) but my pH is around 7.8-8.0. Both ammonia and nitrite still at 0. I got a new Calcium test kit, and it shows 520 (wow--is that alot???) Being on the ditzy side, my first reaction was to freak out. Then, I returned to normal, and decided to post here. You've always been so helpful. So...what do I do?

BTW: 10G with ~30lbs LR and ~30lbs LS; 1 yellow goby, 3-4 mushrooms, 2-3 palys, 1 rock anemone, 1 small frogspawn coral, and 1 moon coral, plus several snails, 3 teeny porcelain crabs & 1 emerald crab. I have 96W of PC lighting, 1PH, and a 105 Fluval cannister which I clean every week.

[Kurt_Nelson]

Are you testing your pH at the same time of day when you test? pH is at its lowest in the morning, just before your lights come on, and then at its highest in the evening right after the lights go off. It's not uncommon to get a 0.2 swing between morning and evening. Other than that, I can't think that just adding a DI section to your RO unit would alter anything in the water that much to cause a pH swing.

Regarding the Ca test... what brand is it? What brand salt you using, and at what specific gravity? You're correct... 520 is a lot. If you're not testing for alkalinity, you probably should if you're testing for Ca. The two go hand-in-hand...

http://www.advancedaquarist.com/issues/nov2002/chem.htm

[fijiwigi]

Originally Posted by Kurt_Nelson

Are you testing your pH at the same time of day when you test? pH is at its lowest in the morning, just before your lights come on, and then at its highest in the evening right after the lights go off. It's not uncommon to get a 0.2 swing between morning and evening.

I have read this before and have always wondered why it is that this happens what is affecting the PH swing??

[LynnCeeBee]

Actually, I normally measure in the mornings, but after lights have been on awhile. Thus said, I decided to remeasure this morning after reading Kurt's reply. ....it's closer to 7.8 this morning, where last night it was closer to 8.0. My previous tests were normally 8.2 or 8.3. I didn't think that the RO/DI unit would cause the shift, but wanted to throw that in because it was the only change from last week. ...Here's the other thing, my 125g tank, which lives and breathes with the same water, still measures 8.3 this morning.

As for measuring the alkalinity, the only test I have for that is the dip strips I'd bought last year. The alkalinity pad measures around 120-130. I don't understand that measurement, because reading that alkalinity/calcium article, I was confused to see that the measurements they take regarding alkalinity use numbers between 0-6. The calcium test I used was an API bottle.

[fijiwigi]

I too use an alkalinity test that uses that scale(hagen) the acceptable KH range is 125-200. Most people use the other scale I have wondered how to convert the #to the other scale.

[Kurt_Nelson]

Originally Posted by LynnCeeBee

Actually, I normally measure in the mornings, but after lights have been on awhile. Thus said, I decided to remeasure this morning after reading Kurt's reply. ....it's closer to 7.8 this morning, where last night it was closer to 8.0. My previous tests were normally 8.2 or 8.3. I didn't think that the RO/DI unit would cause the shift, but wanted to throw that in because it was the only change from last week. ...Here's the other thing, my 125g tank, which lives and breathes with the same water, still measures 8.3 this morning.

Hmm... that is weird. I'm guessing the pH shift is just coincidental to your water source change. Are you using any phosphate reducing media (Phosban, Rowaphos, etc)? I've read that in certain conditions, those can cause a slight drop in pH. Other than that, not sure what's causing the slide in pH...

The calcium test I used was an API bottle.

I've used both API and Salifert for calcium tests. The API seems to be more fussy and I've ended up with readings before that don't make sense. But after repeating the test, I usually end up with better numbers. The API and Salifert tests seem to agree within 20ppm in my experience. I'd just clean out the tubes good (no soap) and rerun the test. Unless you're running really high specific gravity Oceanic salt, that number seems a little out of whack.

[Kurt_Nelson]

Originally Posted by fijiwigi

I have read this before and have always wondered why it is that this happens what is affecting the PH swing??

In a nutshell, when the lights kick on and things start converting light to energy (photosynthesis from algae, etc) they use carbon dioxide (CO2). The decrease in CO2 drives up pH while the lights are on. BUT... the things in your tank also generate CO2 all the time, thus driving down the pH. The combination of those two things cause the normal up/down cycling of pH.

Here's a good article...

http://reefkeeping.com/issues/2007-05/rhf/index.php#6

[LynnCeeBee]

A good article, but now I'm really not sure what to do! I realized I'd done something else in the last week.....I covered my old house windows (which were really leaky) with that shrink wrap plastic stuff, and after reading that article, I thought "Uh-oh." I also removed the aquarium lid last week to do a little maintenance, and left it off. My normal PWC and topoff schedule is coming up, so I measured the pH of my RO/DI water, and it's 7.4. If I add that as topoff water, it's going to lower the pH even more, isn't it?

What would you guys do as a first step?

[Kurt_Nelson]

I normally don't worry about the pH of my topoff water, but maybe it's different thinking with nanos. It wouldn't surprise me that covering the windows might be doing it. Leaving the lid off should help things, because it will help with the gas exchange at the surface. Perhaps reposition a powerhead to give you more surface ripple and oxygen exchange at the top of your tank?

[LynnCeeBee]

Yup....it had to be the windows! I repositioned my PH. The PH also came with an oxygenator that I never bothered to use, so I stuck it on, and let it oxygenate the water. After the repositioning, and a day of the extra oxygen, I measured my pH. It's back to 8.3.....

Thanks! I couldn't believe it came from something so seemingly disconnected from the aquarium.

[Kurt_Nelson]

The air tube on the powerhead isn't doing anything. It can't hurt, but it doesn't oxygenate the water like in a freshwater tank. In saltwater, the oxygen exchange happens at the surface. That's why you want surface ripple, and why you want to stay away from deep, odd shaped tanks (less surface area per water volume for gas exchange.)

I've read lot of other stories from folks that experience pH drop right after summer is over and close up all the windows that'd been open all summer. It surprised me when I read about it, but it obviously has an effect.

Glad it worked out, but keep an eye on it to make sure that the solution was really the solution!