Interesting Case

[Delphinus]

Given that he is dosing Mg then I would agree with your last assessment. But also:

I believe the full 400ml is added at all at once which could be an issue.

I think that is probably it right there, or at least that should be confirmed is the case how it's being added. At the best of times that's quite a sawtooth wave happening, that quick rise in levels is going to have an effect.

[PoonTang]

The Unbaked version (#2) of Randys recipe is the normal one to dose when using Kalk, although i dont know if this would cause any issues. The thing that seems so wierd to me is that he has to add it in such an un-balanced proportion. The 2 part recipies are meant to be dosed in equal portions but he is dosing double the alk as should be needed. Makes me think that something is way outa wack.

[PoonTang]

Originally Posted by Delphinus

Given that he is dosing Mg then I would agree with your last assessment. But also:



I think that is probably it right there, or at least that should be confirmed is the case how it's being added. At the best of times that's quite a sawtooth wave happening, that quick rise in levels is going to have an effect.

I would disagree based on personal experience. I have dumped far more than that in my sump with only a short time between the Cal and Alk being added and never have any precip problems. However if his levels are actually way higher than is indicated than it could be a problem.

[Coleus]

You should try to test his water with your test kits and see the reading. My tank is about the same size as his, I also use Mag 1800 and I have not cleaned it for months. I did not clean my return pump for 2 year with my old one until the front plate got broken :-)

I dose around 80ml for both calc and alk with Randy recipe. But only have small- medium sps corals right now.

[asylumdown]

The only time I got precipitation was when I was doing twice the alk as the calcium, and then I was only adding 150ml of alk to 75 calcium and my pumps were fried in a matter of weeks.

This is first year chemistry:

It's an equilibrium reaction. Calcium carbonate isn't totally insoluble, it's just highly insoluble under normal conditions (like a Ksp of 4.0X10-9 or something). At any given moment in all of our tanks, a small amount of very soluble calcium and carbonate ions are reacting with each other and precipitating out. If things are in balance, the amount that precipitates out equals the amount of calcium carbonate that dissolves back in to the water, favouring the aqueous states of carbonate and calcium. It looks like this:
<-----------------------------------
1Ca(2+) + 1CO3(2-) <----> 1CaCO3

This is highly simplified standard temperature & pressure equation, and when things are normal, you need to worry about pH, carbonic acid/bicarbonate levels, magnesium levels, reaction of carbonate with other ions, uptake by corals, etc. to determine the exact nature of that relationship and how much calcium carbonate you'll produce. But in a balanced system, those other elements that affect that reaction will never lead to pump failures. We're talking about affecting the appearance of molar quantities of calcium carbonate so small you will never, ever notice it in a balanced system (and can barely even measure outside of a lab).

He's adding so much of each, and in such disproportionate ratios, that none of those other, more subtle elements are going to matter. When you provide a gross excess of either of those ions in a solution, you shift the arrow of that equilibrium reaction so that it looks like this:

------------------------------------->
1ca(2+) + 1CO3(2-) <----> 1CaCO3

all the other factors, pH, the relationship between carbonate and carbonic acid/bicarbonate, magnesium levels etc. - none of that matters if you dump so much of one of the primary ions in the above reaction in to the water that you shift the equilibrium way to the calcium carbonate side. Those things are still going on and are important in balanced systems, but the net result of what he's doing is exactly what he's seeing, ruined pumps on a weekly basis.

He's spending money on additives to plate his tank in calcium carbonate.

If I were him, I would stop dosing all additives until things have balanced themselves out. His levels will crash, which will be stressful on the system, but once they're down he can start bringing them back up in a balanced way again.