Why is Kalk so hard to dissolve?

ScottB

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Yes, if you demand is not that high.

Another moral of the story is that dosing from reservoirs is often able to deliver more. :)
Yeah, I think it would be a different story without the 2-part dosing. Tweaking dose levels for either the kalk or 2-part via APEX is so quick and simple.
 
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Dkeller_nc

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One note about conductivity probe cleaning. Scientific/industrial conductivity probes are typically made with platinum-plated electrodes. The platinum coating is used because it is highly resistant to corrosion, but far easier to work with during manufacturing than gold (the most resistant-to-corrosion metal). I don't know for certain that hobbyist probes would have platinum electrodes, but since the cost of setting up a different manufacturing process just to save material costs for hobbyist-type equipment would be prohibitive, it's likely that all of ours are platinum electrodes.

The typical solution for cleaning platinum conductivity electrodes is so-called piranha solution - 3:1 concentrated sulfuric acid to 30% hydrogen peroxide. Both of the constituents of piranha solution would be quite dangerous for a hobbyist without scientific laboratory experience to use. So don't - 30% H2O2 is really nasty stuff (as is concentrated sulfuric acid).

For a conductivity probe that's installed in a kalk reactor, the fouling components as Randy noted would be calcium carbonate. So the sort of materials that hobbyists typically use to clean calcium carbonate deposits off of other equipment are suitable - e.g., citric acid or vinegar. For a conductivity probe used in the actual tank/sump, organic materials will be present in addition to (probably) calcium carbonate. Probes used in this location can also be cleaned with citric acid and a gentle abrasion with a soft brush and a neutral detergent solution such as Dawn/Joy dishwashing soap. Tougher organic deposits can be cleaned with an overnight soak in a basic solution, such as 0.1N sodium hydroxide.

There are a couple of common materials that reefers tend to have around that I would not recommend be used to clean platinum electrodes - bleach and hydrochloric (muriatic) acid. The reason to avoid using either is the presence of chlorides in the solutions. At least in theory, a long soak in either may etch the platinum electrodes - a little etching can be used to clean surfaces, but the exposure time, temperature and concentration is important and generally beyond the knowledge base of typical hobbyists.
 
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Dennis Cartier

Dennis Cartier

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Phew, I used vinegar when I saw Randy mention 'weak'. I could have used citric acid which I also use.

This has got me thinking about my other EC meters. I have 3 Thermo Orions that I have collected up, and have not cleaned the probes. The probes for the Orion's are quite expensive. For my most modern meter, I splurged on a new probe and it was a few hundred dollars.

I do have a few probes on hand for the Orion's that I concluded were bad, but now I am wondering if cleaning them for deposits might restore accuracy. Oh, have to clean them and see.

Dennis
 

Dkeller_nc

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They're probably OK (after cleaning). PH, dissolved oxygen and ORP probes contain membranes and/or crushed glass junctions that will eventually be fouled beyond cleaning, and the probe and/or membrane must be replaced. But conductivity probes are just two metal electrode surfaces with a defined gap in between. As long as the electrical connection to the electrodes within the probe are intact, they typically can be effectively cleaned and recalibrated, and last for years.
 
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Dennis Cartier

Dennis Cartier

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My first attempt at resurrecting a thought to be bad probe was unsuccessful. I have a 011050 2 electrode probe that I had planned to use for monitoring my kalk saturation. It's range is 1 uS/cm to 20 mS/cm, so I figured it would be perfect. Before the cleaning, it gave some very low readings. Placed in my sump which should max it out as it is 53.1 mS/cm currently, resulted in a reading in the 16's. I cleaned it, placed it in my kalk and got a reading in the 2's, but should have registered 8.0 mS/cm, so still fubar'd. Ah well, whatever it's problem is, it isn't that it has a carbonate film.

Dennis
 
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