DIY your own dKh, it's really easy and idiot proof, get dry Ca and Mg if you can as it is much cheaper. Best price I have found is on Brightwell Aquatics, but I haven't shopped around in a while so there might be something else out there now. I wouldn't spend $ on a doser for that small a tank, just dose a bit in between your water changes to help keep up. If you are looking for a cheap doser for lighter duty work check out Marine Magic, but I would say you get what you pay for... I have three
Dan
Dan