Rate of media consumption in calcium reactors

[foxt]

I know that the rate of media consumption is dependent upon the pH of the water, but I am wondering if it is also dependent upon the amount of media in the reactor? What is the relationship of consumption rate, volume, and output dkH?

If I hold the effluent rate and the CO2 bubble rate the same, do I get more, less, or the same dkH out of the effluent in a full reactor vs. one with only 25% of the chamber full? If the pH is set by the flow through the reactor and the amount of CO2, then if there is more media available to melt, won't I get more dkH out of a reactor with more media in it?

Or is the volume of media irrelevant, because for any given set pH, only so much media is melted and that amount is always small enough to make the fill level irrelevant until the chamber is almost empty? Can I really wait until the media is almost exhausted before I refill the reactor?

As my media has been consumed, I am having to bump up the effluent flow rate to keep the tank stable. I know that some of that is driven by increased alkalinity consumption by the coral, but it seems to be ramping faster as the media level gets lower. Coincidence?

 

[JDtimk]

I would think because the water is recirculated in the reactor and the effluent is usually a slow drip, that the pH would be the deciding factor on the dKh of the effluent. Interesting questions though. I am also curious.

 

[blackgrouper79]

I just picked up a reactor myself. How have things been going since this posting? Very curious?

 

[Potatohead]

It is normal for the dKH of the effluent to fall slightly as the media is depleted. Most people refill around 1/2 - 2/3 full for that reason.

 

[Randy Holmes-Farley]

I would think because the water is recirculated in the reactor and the effluent is usually a slow drip, that the pH would be the deciding factor on the dKh of the effluent. Interesting questions though. I am also curious.

It is an important factor, but not always the only one.

 

[Randy Holmes-Farley]

I know that the rate of media consumption is dependent upon the pH of the water, but I am wondering if it is also dependent upon the amount of media in the reactor? What is the relationship of consumption rate, volume, and output dkH?

If I hold the effluent rate and the CO2 bubble rate the same, do I get more, less, or the same dkH out of the effluent in a full reactor vs. one with only 25% of the chamber full? If the pH is set by the flow through the reactor and the amount of CO2, then if there is more media available to melt, won't I get more dkH out of a reactor with more media in it?

Or is the volume of media irrelevant, because for any given set pH, only so much media is melted and that amount is always small enough to make the fill level irrelevant until the chamber is almost empty? Can I really wait until the media is almost exhausted before I refill the reactor?

As my media has been consumed, I am having to bump up the effluent flow rate to keep the tank stable. I know that some of that is driven by increased alkalinity consumption by the coral, but it seems to be ramping faster as the media level gets lower. Coincidence?

I can give the relationship in verbal terms, but you will never see an equation that describes this very, very complicated kinetic chemistry.

The main issue is that calcium and carbonate dissolve from surfaces of the media, and may even dissolve mostly from specific places on the surface (like the edges and corners of planes of crystals). The rate at a given pH depends on the surface area. More surface area (from more media) leads to faster dissolution, at least until (and if) the water becomes saturated with calcium and carbonate.

Higher flow over and through the media can also increase the rate of dissolution because it reduces the chances of an excess of calcium and carbonate being present in the near surface region of the media, relative to the bulk water a millimeter away from the media.