This is basically the same design I use on my tank but I use a 4 gal container and dose in the sump next to my return pump which shoots right into the main tank.
If you are concerned about dripping kalk too fast just use a weaker solution of kalk. It will take you some time to figure out your evap rate and calcium, pH, alk needs with any system you employ. My tank loses about a 1/2 gal a day. I mix 1 teaspoon hydrated lyme per gal and mix about 2 gal every time I refill the doser. One thing to watch is your evaporation rate especially if your water needs increase and you unknowingly continue to mix the same concentration of kalk.
This 'may' have happened with my system during the summer. I was dosing kalk via my vaccuum gravity doser. I was maintaining great ca, pH, and alk values using the same mix. Summer came and my evap rate increased with the increased tank temp. I continued mixing the same batch of kalk BUT it was being dosed quicker. My alk dropped and I'm still bringing it back up. I'm still not sure if this is the reason my alk dropped though, but it is somthing to remember when using a doser like this.
I haven't noticed the salinity increase in my jug through diffusion. I've only tested it twice though, just checked it now. The kalk dregs didn't even register on the swing arm hydrometer. My last dosing session was started during the weekend.
[ October 02, 2001: Message edited by: fishfarmer ]