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.