Kalk to 2-part dosage

[Jwheld]

I currently use Kalk in my auto top off and I'm implementing a 2 part dosing pump this weekend. I'm looking to get my consumption close to start with. Please let me know if my thinking/calculations below are applicable to translate between the two.

Ca(OH)2 + 2CO2 <=> Ca2+ + 2CO2
Tank usage of Kalk is about 0.7tsp/day with total water about 50 gal (190L)

0.7tsp * 2.1g/mL * 4.93mL/tsp = 7.25g Ca(OH)2/day

7.25g Ca(OH)2 * 40.1 g Ca/74.1 g Ca(OH)2 = 3.9 g Ca/day

3900mg Ca/190L = ~20ppm Cal/day

Using 7 ppm Ca/1 dkh consumption ratio I would be consuming 2.9 dkh per day.

This seems high for a lightly stocked tank with no coralline.

 

[bertoni]

That seems too high. Is the tank getting fully saturated Kalk? We could compute from that.

 

[Jwheld]

That seems too high. Is the tank getting fully saturated Kalk? We could compute from that.

No, it's about 0.7 tsp per gallon. I get about a gallon of evap a day.

 

[bertoni]

So by my math, that's something like 0.75 dKH per day. I used the calculator to get a rough estimate:

http://reef.diesyst.com/chemcalc/chemcalc.html

It takes about 1 g of saturated limewater to raise the dKH of 50 about 2.3 dKH. Your solution is at about ⅓ of saturation.

 

[Jwheld]

Awesome! After I stopped Kalk last night it went down around 0.4 doh over 12 hours so I set my pumps to do just less than 0.8dkh per day (equal ml of alk and calcium) and I'll check tomorrow see what adjustments will be needed. Seems like I should be awfully close though.

 

[bertoni]

Yes, that should be very close. The consumption rate might change some, though.

 

[Jwheld]

I wasn't too far off! Tested the tank after 36 hours of dosing and my Alk went from 8.8 to 9 and calcium stayed the same at 425. Adjusted the pumps accordingly. I will probably test the next couple days before chasing my tail and continued tweaking.

I now have that calculator bookmarked. Way more thorough than the BRS one I've been using.

 

[bertoni]

That's very close, indeed. Hopefully, any final tweaking will be just as easy. I'd be careful about noise in the test kits, at this point.

 

[Jwheld]

It's been right on the past 2 days. Alk at 9.0 and cal at 425. I figured it would take weeks to dial in! Now just waiting on growth.

 

[bertoni]

Okay, I hope the corals get to work soon!