$200 to spare--kalk stirrer or 2 part w/ dosing pumps?

[Origami]

(Repeating myself from another thread....)

Here's a *simple* ion-for-ion analysis using BRS prices available today. Let's start with two-part:

 

Calcium Chloride (dihydrate):

Calcium Chloride is what you use to supplement calcium. CaCl2*2H2O lists at $10.99 for 3.5 pounds. At 147.014 grams per mole, that's $10.99 for 10.8 moles of the stuff. Or, $1.02 per mole of usable calcium supplemented.

 

Sodium Bicarbonate:

Sodium bicarbonate is what you use to supplement alkalinity. NaHCO3 lists at 10.99 for 4 pounds. At 84.01 grams per mole, that's $10.99 for 21.6 moles, or $0.37 per mole. However, you need two units of bicarbonate for every unit of calcium, so this brings the price to $0.74 per 2 moles of bicarbonate supplemented.

 

Material cost of two-part, neglecting delivery means is therefore ($1.02 + $0.74 = ) $1.76 per mole of calcium carbonate skeleton.

 

Let's now look at Kalkwasser, or Calcium hydroxide.

 

Calcium Hydroxide:

Calcium hydroxide is a balanced additive. Through a reaction with carbon dioxide (CO2) that is available in the water, it adds calcium and bicarbonate (HCO3-) in the required proportions. In other words, you get two units of bicarbonate for every unit of calcium delivered. So it's sufficient to calculate the cost per mole of that one material to cover both needs. BRS lists Ca(OH2) today at $7.99 for 2.25 pounds. At 74.093 grams per mole, it costs $0.58 per mole of calcium carbonate skeleton.

 

Conclusion:

Ion-for-ion, kalkwasser compares very favorably to two-part in operating costs. Quantitatively, kalk is approximately 1/3 the cost of two-part (ion-for-ion).

($0.58 / $1.76) ~ 1/3

 

Caveats:

This calculation uses current BRS prices for their pharmaceutical grade materials. You can reduce the cost of any of these components with "kitchen" substitutions. For example, in my mind, there's no reason to not use Arm & Hammer baking soda rather than pharma-grade sodium bicarbonate. On Amazon (today), A&H costs $4.49 for 4 pounds, or $0.30 per 2 moles. This alone can reduce the cost of two-part to $1.32 per mole. Still more than Kalk, but a savings nonetheless. Additional (and even greater) savings may be gained if you find an acceptable grade of commercial ice melt that is relatively free of unwanted impurities - keeping in mind (of course) that most grades of ice melt are calcium chloride HEXAhydrate CaCl2*6H2O (which is 219.08 grams per mole, and therefore only 67% as dense as the dihydrate material) which means you'll use about 50% more of it for the same calcium boost. The same applies for calcium hydroxide, though, which can be obtained in bulk quantities as Mississippi lime, for example.

 

Another fact that might help put this in context:

Assuming a coral skeleton is 100% calcium carbonate (and it's not - it varies typically between 85% and 98% depending upon the coral and the environment), one mole of calcium consumed plus two moles of bicarbonate consumed are required to produce 100 grams of coral skeleton since calcium carbonate - Ca(CO3)2 - weighs 100.09 grams per mole. Depending upon your dosing method, this growth can cost you $1.76 (using two-part) or $0.58 (using kalk).

[ctenophore]

I simply add kalk to a 5 gallon topoff bucket on my 29 gal sps tank. I control this with both a float switch and a pH probe (both on AC3). I have found this to be a safe, reliable way to maintain salinity, calcium, alk, and pH all at once. All of the sps are still small so I can see this tank needing 2-part in time. I add the topoff kalk water via single BRS dosing pump controlled by a DC4. I will eventually add a stirrer to this setup. I meet the alkalinity demand by varying the amount of kalk powder I add to the 5 gallons of water, usually 1, 1.5, or 2 tablespoons. Interestingly, I've found that with the pH ceiling set to 8.45, which is where the tank pH stays 24/7, alkalinity seems to be stable at 9.5 DKH. This is odd because the two are not really related, but I can't seem to get the alk any higher than that, regardless of the demand. I suppose this is a good thing.

 

The only accident I have had with this system in 2.5 years of operation is when the tube on the output side of the peri pump got clogged, and the pump blew the tube off the barb fitting near the roller. Result was about a half gallon of fresh water on the wood floor. Other than that, it has been a safe kalk delivery system for the inhabitants. The dual negative feedback control loops help prevent kalk overdoses.

 

Total cost for this system was $80 for the pump, $7 for float switch, everything else I had laying around. Kalk cost is pennies, maybe 5 tbsp/month, max. I suppose the AC3/DC4 kit should be factored in, but that also controls lights, temp, etc so maybe factor $100 for pH probe and a share of the AC3. I'd recommend this control system for any automated ca/alk dosing system, whether 2-part, kalk, or CaRx, as any of these methods could lead to overdosing. The peri pumps are highly reliable but if you rely on a cheap timer to turn them off and on, that is a point of weakness IMO.

 

I guess the point of this post is don't necessarily factor only the cost of the equipment and consumables, but also the failsafes necessary to insure against accidents (which could cost you a lot more than the initial setup!)

[Stu]

Wow. Thanks everyone for the input, and detailed analyses. I decided to buy DonP's GSA stirrer, as I couldn't refuse the price. I was really happy with the results when I was running a stirrer before, so I'm gonna see how it does again with the new one. I also found a seller on ebay who sells 2-channel adjustable flow rate dosing pumps for about $80 (don't need to buy 2), so I will probably try running the stirrer and 2-part together at some point. At that price, I figure it's worth a shot.

[ctenophore]

I also found a seller on ebay who sells 2-channel adjustable flow rate dosing pumps for about $80 (don't need to buy 2), so I will probably try running the stirrer and 2-part together at some point. At that price, I figure it's worth a shot.

Link?