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View Full Version : Help please understanding ALK


mr.maroonsalty
12/28/2009, 01:32 PM
I've seen posts of people worrying about 12-15 dKH lately; aren't Alk readings more or less an expression of the waters ability to resist change in pH? In a balanced system is there a corresponding Ca level for any given dKH reading? From a reef Chemistry pov what is high Alk and its impact on the tank? Thanks

HighlandReefer
12/28/2009, 01:53 PM
The term "ionically balanced" in most cases comes from the idea that reef inhabitants such as coral use alkalinity and calcium at the same proportions. So to maintain your alk and calcium you will need to add supplements once your tank parameters are where you want them at this same proportion.

There is no correct calcium level for a given alk level as far as the concentrations in your actual tank other than maintaining the calcium and alk between those levels recommended as guidelines. For alk 7-11 dKH and for calcium 385 ppm - 450 ppm. Many hobbyists decide to keep their levels higher or lower than the recommended guidelines though.

The higher the alk, the greater the buffering capacity of your tank water. This means that at higher alk levels your tank will not suffer as great a pH swings as at lower alk levels. However, at higher levels of alk. (above 12 dKH) your tank will produce more calcium carbonate deposits on your tank glass and equipment. These calcium carbonate films can be difficult to remove. You will need a lot more alk supplement to maintain these higher alk levels also due to the increased precipitation.

At higher alk levels coral will grow their skeletons faster, which has been demonstrated in research. For coral to maintain tissues around the increased skeletal growth, they will need more nutrients to keep up. So low nutrients system may not be adequate and result in burnt tips or other possibilities.

So there are some trade-offs if you wish to maintain alk levels higher than 12 dKH.

HighlandReefer
12/28/2009, 02:00 PM
FWIW, Randy has some ideas for maintaining higher alk levels and reducing the calcium carbonate deposits formed by the higher alk levels. The implications for this might be increased coral growth for coral farmers. ;)

You will have to wait til Randy comes back from vacation to ask about this, since I don't remember the details discussed. :)