If you're looking for a single doser with a slower drip rate I recommend the Accudoser II Reef Doser from Oceanic Corals. I've had it running for a couple of weeks now and I'm very happy with it. At 1.5 ml per minute it takes 2 hours to drip the 180 ml of alk my tank requires. And at only $80 it doesn't break the bank.
I tested it with water three times and got exactly the same volume per 2 hours running time. Filll a 1/2 gal container with BRS soda ash, program the doser through the controller and I'm good to go for 10 days before refilling.
