Calcium Reactor Experiment

[Weatherman]

I got a Pinpoint pH Monitor a few days ago and was quite surprised when I let in run on my 120g tank. The pH swings from around 8.22 during the day to 7.94 at night. I can only conclude this is due to dissolved CO2 from the calcium reactor, since the pH in my other two bare-bottom tanks only swings from around 8.2 during the day to 8.1 at night.

So, I’ve decided to run an experiment with my calcium reactor.

Given that:

1) Only a very tiny fraction of CO2 injected into a calcium reactor is converted into carbonic acid, and the reaction is relatively slow, and

2) Once the pH shift from the carbonic acid creation drops the carbonate concentration below saturation, it takes a while for enough reactor media to dissolve to get carbonate levels back to saturation again…

The hypothesis is: The best effluent flow rate is the absolute slowest that can possibly be set and still keep up with alkalinity demand.


Over the next couple of weeks I’m going to gradually decrease the effluent flow rate and increase the CO2 bubble rate on my calcium reactor in order to maintain the same meq/day alk delivery rate.

Assuming the hypothesis is correct, I should see the minimum pH values in my 120g tank slowly climb, while the alk remains constant. The reduction in CO2 delivery should also slow down the growth of algae.

I’ll start to make the adjustments tonight and post the results every few days.

[Wiskey]

Great experiment! If you can get the reactor to that line right before the media turns to mush, you should be able to push the effluant drip rate rather low I would think.

Whiskey

[Weatherman]

Just as a reference, for the tuning-a-calcium-reactor-by-monitoring-pH fans out there...

Starting effluent pH is 7.1

[Leonardo's Reef]

Weatherman, what is the pH inside your reactor?

Leonardo

[Weatherman]

After Friday evening's reset, it's now down to 6.98 (was 7.10).

I'm going to let it stabilize for a couple of days, then make another adjustment.

[Weatherman]

I gave my effluent drip rate another tweak down yesterday evening. The effluent pH is now running 6.85. The effluent flow rate is now very slow at around 7 ml/min.

Interestingly enough, the changes I've made to the calcium reactor have had absolutely no effect on the tank water's pH swing.

Is the null hypothesis going to prove correct?

[Weatherman]

After a week of running the reactor with an effluent pH of 6.75, the pH swing in the tank water is 7.97 at night to 8.30 during the day.

The conclusion drawn from the experiment is that there is a very small benefit to running a calcium reactor with a lower effluent pH and slower flow rate, but not enough to justify an adjustment if things are working ok at the original settings.

[Viv]

Did you notice any change in the algae growth?

[Weatherman]

Seems to be a little less aggressive growth, but I'm going to wait a couple more weeks before reaching any conclusion.

Since the calcium reactor has been discounted as the cause for the big day-to-night pH swing (my other two bare-bottom tanks only swing about 0.1 to 0.15 from day to night), the only other thing I can think of causing it is the sand bed I put in the sump. The sand bed's about a year old, and has never been stirred, so it's well established.

As Spanky has said, a sand bed can be considered the largest single organism in a tank. When a sand bed speaks, the tank listens.