Planted Biocube 8 Journal Pt. 2

[Ambidestrian]

This is the continuation of this thread.

So I bought a Biocube 8, changed the lighting to 1x6500K and 1x10000K, made a couple modifications to the filter including a quieter pump with higher flow rate and replacing the bioballs with sponges and filter pads, and putting a pre-set 76 F heater in the first chamber.

The substrate is a ~3 inch layer of Eco-Complete.

The CO2 regulator arrived today, and I decided to begin experimenting with the CO2 to reach my target value of 30ppm.

The procedure I will use is as follows:
-Buffer the (RO) water with 0.001M NaHCO3 (0.084g/l=~0.32g/gal or about 1.28g for the 4 gallons of water volume in this system.)
-Verify the KH with a KH test kit (accurate to 1 degree)
-Set the CO2 to a set flow rate - beginning with 1 bubble/sec
-Record the pH at 30-minute intervals to calculate the concentration of CO2

Results to follow.

 

[Ambidestrian]

At t=0, KH= 1-2 degrees (this test is not accurate [1 drop = 1 degree KH] and was a waste of money unless I use it to titrate larger samples.) pH = >7.6.

Adjusted CO2 flow to 60 bubbles/min and am using the return pump for a diffuser, incorporating the venturi attachment provided with it.

t+ 0:30 - Bubble rate: 56 BPM pH: 7.4 [CO2]: ~5ppm
(oops)
t+ 1:30 - Bubble rate: 49 BPM pH:6.9 [CO2]: ~15ppm

Nudged the pressure regulator knob CW to increase pressure and compensate for downward drifting bubble rate. Went back up to 54 BPM and I didn't want to mess with it. Going to the store to get a check valve. I will probably have to increase the pressure after adding the check valve.

So, it appears that this 1 bubble per second is initially raising the CO2 concentration by 10ppm/hr. Eventually, it will reach an equilibrium - the CO2 will not dissolve as readily and the rate of offgassing into the atmosphere will be higher and the rate of CO2 influx will equal the rate of CO2 efflux. I am going to let it run like this for a few hours, test the pH again, and gauge whether I am reaching an equilibrium by comparing the value expected from a linear 10ppm/hr increase with the actual value.

 

[Ambidestrian]

I purchased an Elite brand check valve featuring "low resistance to air flow" and installed it. Doing so cut the flow rate approximately in half. I had to increase the pressure significantly to increase the flow rate to 65 BPM. The pressure is slightly higher, so I think I may be actually getting proportionately more gas into the aquarium. I should have installed the check valve first.

One note about the Miluwaukee 957 regulator - adjusting the pressure provides finer control over the flow rate than does adjusting the needle valve.

 

[Ambidestrian]

t+3:00 - pH: 6.8, [CO2] = ~20ppm

It looks like ~60 BPM into the venturi will probably be about the right rate, since if the concentration of CO2 were steadily increasing, 30ppm would be expected. I believe this system will be less prone to disturbance from CO2 uptake by plants because fewer bubbles seem to be fully dissolving - this suggests that with the large bubbles produced by the venturi, the decreasing solubility of CO2 as the concentration thereof rises plays a major factor in the shape of the concentration vs. time curve.

Since CO2 is only $3/lb, I find it difficult to justify spending money on a more efficient diffuser. The tank should last several months at this rate, and costs $15 to refill, plus this system is more resistant to fluctuation that would be a 100% efficient diffuser. I imagine that might save some CO2 on a very large aquarium.

The lights go off in 3.5 hours at t+6:30, so I will check the pH again then; I interpolate that it will be near the maximum value then.

[NO3-] is ~15ppm, indicating that nearly all the originally added NH4Cl has been processed and that the nitrogen cycle bacteria must have a good foothold in the tank - at least enough to support the bio-load from a single, small fish. I think I'll hold off on moving him until the plants arrive. They should ship tomorrow.

 

[Ambidestrian]

At t+6:30, when the lights went out and the solenoid closed, the pH was between 6.4 and 6.6. I couldn't read the color accurately under the incandescent light and would have preferred sunlight. It will be light at 6:30 from lights-on tomorrow and I can take a more accurate reading.

6.5 would indicate 40ppm, so I'm in the right ballpark. This is, of course, ignoring the influence of the acid presumably produced through the metabolism of the ammonium chloride, so my estimate for CO2 concentration here is slightly below 30-50 ppm.

The plants' metabolism will probably decrease this a bit. I don't think I will do much adjusting.

Pics coming later this week after the plants are planted!

 

[Ambidestrian]

Today, the bubble rate has slowed to ~30 BPM. Maybe I am understanding what people mean about the miluwaukee regulator, but very few regulators are really consistent at such low pressures. I haven't even moved the needle off of the peg. I wonder, though, if this might be more efficient. I will test again at t+ 6:30 and see what kind of a CO2 level I'm looking at. This morning, the CO2 level was >7.6, indicating <5ppm CO2.

 

[Ambidestrian]

Well, I had a change of schedule, and had to check the pH at t+5:45. The pH was ~6.9-7.0, a [CO2] of ~15ppm. This is significantly lower than my target level at half-way through the light cycle, so I am re-adjusting the output pressure of the regulator to obtain about 60 BPM and hoping it will stabilize around 45-50 BPM.

 

[Ambidestrian]

Milwaukee MA 957 Regulator Behavior Issues

I am beginning to understand the complaints of some using this regulator. After my last post, I adjusted the pressure upwards (the needle valve has remained at the same setting) until the bubble rate was 62BPM. Now, a few hours later, it is down to 53 BPM.
The bad: The flow rate is not remaining constant
The good: The rate is steadily decreasing, rather than fluctuating unpredictably. I posit that this could be due to some initial "break-in" or plastic deformation of the internal mechanism and that it could reach equilibrium and become stable with time.

The pH is now just below 6.6, so the CO2 concentration is between 30 and 40 ppm - right on target.

 

[Ambidestrian]

Again, the rate is slowed; less this time; to about 45 BPM.
I attribute this to the regulator parts breaking in, especially since the rate of change is becoming less.

I am thinking about just buying a pH controller. It is the $/gal figure that dissuades me.

Edit: Also, I read this Second post on this page which made some valid points, IMO.

I installed an airstone underneath the return pump to diffuse the CO2 and it is working nicely - it appears much more efficient than the venturi; I may have to decrease the flow rate. The airstone makes the bubbles small enough they don't make noise when they hit the impeller and they are barely noticeable when they exit into the tank.

I will leave the flow rate as is for now, and tomorrow I shall test the pH at intervals.

 

[Ambidestrian]

Milwaukee Regulator
The bubble rate has stabilized. I stand by my break-in theory, and this seems like a very decent regulator for the price.

I decided to do away with the air stone and stick with the venturi diffusion method. There were bubbles building up underneath the pump and I could hear them hitting the impeller.

Sweet Aquatics
I ordered a collection of plants from sweetaquatics.com 7 days ago, and they say they will ship on Monday. 10 days from payment to shipping seems like a long time; I hope these are good plants.