Can you explain these odd, Blackout related, pH changes? - The Planted Tank Forum
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post #1 of 56 (permalink) Old 04-20-2008, 06:14 PM Thread Starter
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Can you explain these odd, Blackout related, pH changes?

Three days ago I decided to do a blackout on my tank. That process caused some interesting effects in my pH readings, that I would love to understand. Maybe you can help.

The changes I'm referring to can all be found in the chart below, which is the last 7 days temp and pH readings from my Aquacontroller II. The labels at the bottom of the graphs are crappy, so allow me to explain what you are looking at...



On the left hand side of the top graph you can see a temp spike, followed by a precipitous temp drop, followed by 3 or 4 rapid drops again. That is my tank temp climbing in the evening (room is warm from winter heating) until the tank lights shut off, causing the precipitous drop. The three to four cold spikes following that are the multiple small water changes my tank does automatically every night - the new water is a bit chilly. Then the next morning the temp begins to climb again when the lights are turned on, and continues until its peak, when they are turned off.

That explains the temp for one day. In this graph you can see that pattern repeated for four normal days. The things got wacky when I did the three day blackout.

During the blackout, with black plastic covering the entire tank - even the top - the tank was having trouble throwing off heat. I do not have canister filters, instead I have two external pumps pushing my filtration (primarily Ocean Clear filters) that are very quiet. But the cost of having these silent pumps is that they add heat to the water.

When I did the blackout - the 5th day on this graph - the heat spiked faster than normal, and showed no sign of stopping. That heat was just from the pumps - keep in mind, the lights are normally adding heat, but then they were off. So I shut off one of the two pumps, and as you can see, the tank temp steadily fell to the 82 degrees I keep the heaters at. Over the next two days of blackout, the temps rose again, but not much, then leveled off each night.

I understand the heat... it's the pH that has me scratching my head.


As you look at that heat from the first four days, you can see in the pH graph below that both day and night my pH stays fairly level. A powerful Mazzei venturi to injecting CO2, with a controller on night and day, keeps my pH pretty level.

When I started the black out I shut off the CO2, tossed in a extra airstone, and set my returns to splash up the water surface pretty well. You can see that reflected in the rapid climb in pH as the CO2 outgassed. But one thing that is curious is the rapid pH drop from the peak of 6.9 down to 6.7. That happened immediately after I turned off my 2nd pump/filter combo to reduce the heat. What would cause that pH drop?

As you can see, after the mystery drop, it settled in at about 6.6. But that final dip (which is still continuing BTW) has me curious too. I removed the blackout plastic a couple of hours ago. I did not turn on lights or CO2, though I did remove the airstone.

But as soon as I did that, the CO2 began dropping again - see that dip at the far right side? Why is that happening?

If anything, having ambient light from the room, the plants should be taking CO2 out of the water and driving pH up. Not down.


So, sorry for the long post. But two things have me scratching my head.

First - Why did my pH drop when, during the blackout, I turned off one of the pumps?

Second - Why, after I removed the blackout plastic, did my pH begin to drop again?

Love to know your thoughts. I'm baffled.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #2 of 56 (permalink) Old 04-20-2008, 06:23 PM
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Originally Posted by scolley View Post
As you can see, after the mystery drop, it settled in at about 6.0. But that final dip (which is still continuing BTW) has me curious too. I removed the blackout plastic a couple of hours ago. I did not turn on lights or CO2, though I did remove the airstone.
6.0? I don't see it...sorry if I'm missing something.


Interesting observations...I'll have to give this some thought.
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post #3 of 56 (permalink) Old 04-20-2008, 06:27 PM
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Is that a rollercoaster ride or a discus tank!?!?

First thing that comes to mind is your ballasts are causing interference with electronics. My pH meter will throw funny readings when a near running ballast.
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post #4 of 56 (permalink) Old 04-20-2008, 06:34 PM Thread Starter
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6.0? I don't see it...sorry if I'm missing something.
Sorry. That was a typo. I meant 6.6. I'll fix it in my original post.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #5 of 56 (permalink) Old 04-20-2008, 06:34 PM
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This is random, but could the plants be using the carbonates in the water now that the CO2 has been shut off? Granted, it would be limited because of the lighting also being off, but it was the first thing that came to mind. Is the TDS changing too?

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post #6 of 56 (permalink) Old 04-20-2008, 06:44 PM Thread Starter
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Originally Posted by Brilliant View Post
Is that a rollercoaster ride or a discus tank!?!?

First thing that comes to mind is your ballasts are causing interference with electronics. My pH meter will throw funny readings when a near running ballast.
I suspect you are reacting to how this is graphed. When the temp range is only 4 degrees, and an entire day is crammed into a horizontal inch of data, it looks like wild swinging. But it's not really. It's just not rock solid. I'm willing for my temp to swing some at night to get me out of water changes.

It might be electronics, but it is not the ballast. Keep in mind that both of those pH drops I'm asking about were when the lights were off, and had been off for a while.

Though electronics in general could be a good question. But if turning the pump off was causing a major change in my probe's reading, it should have be instant. Not over the course of an hour or more, as this chart shows. But I will start that pump up again and see if it spikes back up, just as the bottom dropped out when I shut it off. Thanks.


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This is random, but could the plants be using the carbonates in the water now that the CO2 has been shut off? Granted, it would be limited because of the lighting also being off, but it was the first thing that came to mind. Is the TDS changing too?
Actually I think that is brilliant. Would that drive down the pH? As for TDS, I don't have a meter or kit. Can't answer that one.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #7 of 56 (permalink) Old 04-20-2008, 06:47 PM
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If the plants were consuming the carbonates, then yes it'd drop the pH because your KH would be dropping too. Not all, even many really, plants are able to utilize carbonates from the water, but some can... please don't ask me which ones. I would suspect that because the carbonates were being removed from action, so to speak, into the plants, your TDS would drop too. Now if you were to test your KH and it was the same as usual, the theory is crushed.

Oh, and come on now, you have the million dollar aquarium (just kidding) and you don't have a $20 TDS meter?

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post #8 of 56 (permalink) Old 04-20-2008, 07:20 PM Thread Starter
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Originally Posted by Brilliant View Post
Is that a rollercoaster ride or a discus tank!?!?
I should probably mention, those daytime temp spikes are new. I put this 2nd pump in a few weeks ago, and it could be causing it. But we also are into a funky weather pattern where it's cold at night, warm in the day. So the ambient temp in the room climbs. I've been watching this to see if it was a seasonal issue, or that I had to change pumps. That will take another week or two, but I will shortly get back to a point where I do not have the daytime temp spikes.

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If the plants were consuming the carbonates, then yes it'd drop the pH because your KH would be dropping too. Not all, even many really, plants are able to utilize carbonates from the water, but some can... please don't ask me which ones. I would suspect that because the carbonates were being removed from action, so to speak, into the plants, your TDS would drop too. Now if you were to test your KH and it was the same as usual, the theory is crushed.
Luckily I DO have a nice Lamotte KH kit, so I can test that pretty easily. It's pretty accurate too.

I did a test, and my KH about 18 ppm. My water is very soft, and this is something I pay close attention to. Unless I add something to it to raise the KH, it stays at 22 ppm. That doesn't seem like much - but in my tank, that's a real drop. I've never seen it that low.

So I think you may be to something - good job! That is assuming you assume the KH would drop.

And FWIW, I've plugged the airpump back into the same socket. I'm gonna let it run for an hour - with the airstone back in the tank. To see if it has any effect. I suspect it will not. I don't think my turning it off is the culprit.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #9 of 56 (permalink) Old 04-20-2008, 07:25 PM Thread Starter
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Oh, and come on now, you have the million dollar aquarium (just kidding) and you don't have a $20 TDS meter?
I don't have a TDS meter per se... just like I'm not too worried about the temp swings. My discus spawn like rabbits. It's my assumption that that tells me I don't have a TDS issue (or temp) and that I don't need to waste the money. The fish seem happy.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #10 of 56 (permalink) Old 04-20-2008, 07:39 PM
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Yes, I would expect the KH to drop if your plants were consuming the carbonates in the water, it's that KH drop that you would be seeing translated to your pH reading also being lower.

The drop of only 4ppm is not enough to drop your pH that much though... at least I don't think so, I would expect a more dramatic change. I think it's something like half a degree for every 5th of a pH point.

I didn't intend to imply any sort of TDS issue, but more that was a way to correlate results. I'd never want to be without my TDS meter, I'm just surprised you don't have one

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post #11 of 56 (permalink) Old 04-20-2008, 08:05 PM Thread Starter
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The drop of only 4ppm is not enough to drop your pH that much though... at least I don't think so, I would expect a more dramatic change. I think it's something like half a degree for every 5th of a pH point.
Well, I've got more data...

I've got a hand held pH meter that I just calibrated, and it tests bang-on for 7.01 and 4.01 solutions. And the first thing I did when I pulled the sheeting off the tank was to dip a 2 liter bucket in the tank to use as a control for any testing I might do. Boy am I glad it did that.

The control sample reads 6.71 with the hand held, and the tank reads 6.66 with it. So the tank is now off 0.05 from when I pulled the sheeting off. And that is MUCH more in keeping with the minor drop in KH.

Of course that leaves the question of why, when I know this hand held is right, did the pH probe for the AC II read as low as 6.38 a little while ago? Yes, it kept dropping... Right now the AC II says 4.46 and the hand held 6.66.

As I indicated, I plugged the air pump back in, and the pH has started climbing. Just like it started dropping when I unplugged it.

But it can't be electronic, can it? If it was electonic, would my swing not be immediate - rather than the slow drop when unplugged, and slow climb not that it's plugged back in.

This makes no sense... I've gotta go for the moment. But boy, am I still scratching the old head!

PS - No prob on the TDS. I just really don't worry about it as long as the fish keep spawning. I've always figured if they keep it up, that's one expense I don't have to worry about.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #12 of 56 (permalink) Old 04-20-2008, 08:21 PM
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Recalibrate the pH probe on your Aquacontroller? Maybe it's failing? Strange time to have that happen, but it's worth considering.

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post #13 of 56 (permalink) Old 04-20-2008, 08:34 PM
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If you are refering to biogenic decalcification then if that is happening the PH would go up. Biogenic decalcification occurs when there is not enough CO2 and there is high KH and high light levels. I believe that vals can do this. I had a 10 tank heavily planted with vals and I mistakenly left the lights on continously for several days-white deposits on the plants and high ph.


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post #14 of 56 (permalink) Old 04-20-2008, 08:41 PM
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[del]No, I'm not referring to decalcification, this would be more a form of bio-acidification.[/del]

Apparently that was what I was talking about after all...

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Last edited by imeridian; 04-20-2008 at 11:48 PM. Reason: Oops
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post #15 of 56 (permalink) Old 04-20-2008, 08:56 PM
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According to what I can find online about biogenic decalcification the PH would rise until KH is 0 then it would start to drop. But it's driven by light. During a blackout plants would take in O2. What effect on PH would that have?


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