Hi, from memory I used about 5 - 7 drops. I don't think it's so much the quantity you use, as this doesn't take into consideration sample size or other factors. The important thing is to test the sample with your pH sticks (after mixing it up a bit!) to make sure that the pH is down between 4.5 to 5.5. I tried to get mine down to 5 ish, maybe a bit above as I think it gets pretty hard on the old spermies if it's much under 5.
Morkas, it's not unheard of to have to use 12 drops, your DH might have given you a supersized sample! I wouldn't worry as long as you're testing it.