Put kalk powder straight in ASW?

[mathias999us]

Hi Randy,

I've read most of your Calc/Alk articles, and found them all really informative. Thanks to you, I think I have a decent grasp on the subject now.

My question is (which I'm sure has been asked many times before):
While a lot of people say that all salt mixes are the same, or use whatever's available, I find that one definite measureable difference between salt mixes is the alk and calc levels in a fresh bucket of ASW. A lot of brands have the ratio out of balance, while some are just too low. Right now, I'm just using good ol' IO. I find that the calc level in a fresh bucket of IO seawater is ~290-300ppm, and the alk is ~2.8 meq/L (8KH). This seems like it's almost a balanced ratio, but deficient in both (perhaps favoring a calcium deficiency). Would it be acceptable to add Calcium Hydroxide powder straight to my mixing bucket of ASW, giving it time to fully aerate and re-establish the carbonic acid/atmospheric CO2 equilibrium, in order to produce ASW that has acceptable Calc/Alk levels before it ever goes into my tank?

I'm running a nano now, and I'm using kalkwasser in my auto top-off, but not enough evaporation occurs in the small tank for this to be a significant contribution. Additionally, since the nano's primary method of nutrient export is large percentage water changes, it is even more important that the ASW that is going into the system have correct calc/alk levels to begin with.

Based on my understanding of kalk, this should work fine, but I just wanted to verify. Any help or advice is most appreciated.

Mathias

 

[Randy Holmes-Farley]

Those values seem low for IO. What salinity are you mixing to? I've found more like mid 300's and 4 meq/L.

The problem with adding lime is several fold. Primary is that the pH will get too high for any reasonable rise in calcium. Second, the alkalinity will rise by 1 meq/L for each 20 ppm rise in calcium. So boosting calcium by 100 ppm push alk through the roof.

So I'd boost it with calcium chloride, and either not worry about the alk (which at 2.8 meq/L is not bad), or add a little baking soda.

This calculator shows how much of each to add:

Reef chemicals calculator
http://home.comcast.net/~jdieck1/chem_calc3.html

 

[mathias999us]

Hmmm, I'm mixing to 1.026 spg with RO/DI water. Maybe test kits are bad?

OK, thanks for your time and help,
Mathias

 

[Randy Holmes-Farley]

Could just be a differing batch. How was that sg measured?

 

[mathias999us]

Just using a hydrometer... the hydrometer is actually pretty old, may be time for a new one... I'll bring some of the water to a LFS and have them measure with the in-house hydrometer, and if it's different, I'll get another...

 

[Randy Holmes-Farley]

Sounds good.

You can also test it yourself with the standard:

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

 

[mathias999us]

Randy -

OK, I really appreciate you pointing that out. I made the hydrometer calibration standard with 161mL of RO/DI and one tsp of salt, and my refractometer measured the solution as 1.0295, which would cause me to make ASW with a lower concentration of salt than the goal of 1.026. Do you think that this error in my hydrometer would actually account for the size of the difference in alk/calc levels in my IO water than what you would typically expect?

Mathias

 

[Randy Holmes-Farley]

It would move 300 ppm to 340 ppm calcium, which is more typical.

 

[mathias999us]

I bought a new hydrometer, and it confirmed the inaccuracy of my old one. The new hydrometer is spot-on with your calibration standard as well. My pH is always low around here, so aside from the pH concern, and the alk rising too quickly, would their be any other concerns with adding Calcium Hydroxide powder straight into ASW? Are there any unexpected precipitates that will form, cloudy water, etc, vs adding to FW then dosing to the ASW?

Thanks again,
Mathias

 

[Randy Holmes-Farley]

Well, yes, you add more impurities if you dose solids or a slurry than clear settled limewater. Whether that is important or not I can't say for sure.

IIRC, Anthony Calfo is a fan of adding it as a slurry.

 

[mathias999us]

OK, I'm beating this horse to death, but how about if you used a certain (calculated) amount of clear settled limewater to mix up your ASW?

 

[jmicky41]

Dang it, I used Mortons Plain (uniodized) salt for my calibration solution. Will this change my results. Thanks

 

[Randy Holmes-Farley]

OK, I'm beating this horse to death, but how about if you used a certain (calculated) amount of clear settled limewater to mix up your ASW?

To do what? You still can't raise calcium substantially with it. You can raise pH a lot and alkalinity a little.

Dang it, I used Mortons Plain (uniodized) salt for my calibration solution. Will this change my results. Thanks

I expect that makes no significant difference.

 

[mathias999us]

Well, I should be able to use a little to at least raise my pH to 8.3 (it's usually right around 8.0 in a fresh bucket), and have the side benefit of increasing alk a little. I'll pick up some calcium chloride too.

Thanks for being so patient and informative. You are truly gentleman and a scholar.

Mathias

 

[Randy Holmes-Farley]

Thanks.

If you raise the pH, it will only stay up for a while if you aerate the water with high CO2 air. So either add it and use it, or add it and stop aerating the water.