yep, with all the stony you acquired, your levels can drop fast in that tank. I still recommend getting a doser. Keep an eye out on the buy/sell forum in here. You can get a used one for a good price.
In the mean time, dosing by hand is probably better than your thingy. Get a couple measuring cups like this one (the smallest one):
http://www.tapplastics.com/product/p...containers/196
Use them to dose your CA/ALK/etc