Join Date: Nov 2006
Location: Coralville, Iowa
Salts will freely diffuse out of the agar. Larger molecules will as well, though at a slower rate. Once the agar sets, it creates a porous network. This feature is exploited in the use of agarose gels used to analyze DNA fragments by size. Agarose is just highly purified agar that is used by molecular biologists.
These agar-fert blocks might work, but I would like to offer a few suggestions. First, be sure to sterlize your casting tray of choice. (Maybe use an ice-cube tray?). You could do this the way that home-canners sterilize jars by using a boiling water bath or the dishwasher. Boil the solution thouroughly. This is needed to dissolve the agar and keep things sterile. This may not be a good idea for traces because the heat might dissrupt some of the chelation of the traces. If I were in the lab, I would simply pass the trace solution through a 3 micron filter to sterilize it and add it directly to the agar once it had cooled to a reasonable temperature. (~65 degrees C is good. cool enough to handle.) This is the method that I use to add antibiotics and drugs to the agar media that I make. Second, I would do some bottle tests to check the diffusion rate of the ferts from the agar blocks into the water column.
So, in summary, this could work as a way to make dosing blocks for at the very least macros. You could put a small sterilzed stainless steal washer in each block to help it sink. I can't tell you how long a block would last, though.
Oh, and i would not use jello. Agar is a polysaccharide, whereas gelatin is a protein. You do not want decomposing proteins in your tank! Your poor fishies!