Consistency from Calcium Dispenser

[Neal Flomenberg]

I recently installed a calcium dispenser to supplement the Calcium and alk I was getting from my calcium reactor and to offset the drop in pH caused by the CO2 from the reactor. This is in a 75 gallon tank with many LPS and SPS as well as 3 clams.

I initially added only 1 tsp of Ca(OH)2 to the dispenser so as not to overshoot either with regard to pH or Ca++. Over the first few days, I was ecstatic as my pH rose from below 8.1 to 8.3 and my Ca++ was where I wanted it at about 435 for several days without other supplementation. (Alk was around 9)

However, over the next few days, both pH and Ca++ have drifted back down.

I am a bit uncertain as to how the dispenser can maintain a consistent output of Ca(OH)2. You constantly pump distilled water through the container which seems like it would have to steadily dilute the concentration of Ca++ and OH- in the dispenser (and thus what's going to the tank). What am I missing here? I hope the answer is not to add more Ca(OH)2 every few days as my goal was automation.

Also, one customer suggestion re design. If we're adding teaspoons of Ca(OH)2 to the container, it would be nice if a teaspoon could fit through the mouth of the container. Given that Ca(OH)2 can be nasty, don't like getting the powder anywhere but into the container.

Many thanks as always Roger.

Neal

 

[rvitko]

I always just fashion a paper funnel, just roll a piece of scrap paper into a cone.

Calcium Hydroxide has limited solubility in water, only a limited amount can dissolve and saturation is reached. When new water is added, more is dissolved. The dispenser protects the solution from exposure to CO2 which will form CaCO3 which will precipitate and weaken the solution. The only way to make a stronger solution is to mix a slurry, which is what the bigger motorized dispensers do, or increase the solubity by adding some vinegar to the container- you can find more about this in the chemistry forum here on RC, or by heating the water, adding the powder and cooling it- this makes a very unstable super saturated solution.

 

[Neal Flomenberg]

Understood. Given the limited solubility, why not add a bit more and be able to go longer without messing with the container?

 

[rvitko]

You can but if you add a large amount the risk of dosing a slurry that may cause a precipitation reaction is higher.

 

[smatter]

I unscrew the cap, draw out 50ml of water with a syringe and squirt it into a small beaker into which I have put the lime. After a brief stirring with the end of the syringe it easily pours into the opening on the dispenser with no mess.