Hedrin does not kill the eggs. Even the manufacturers admit that.
The only thing that is effective against eggs is the Nitty Gritty.
Tink. Once I got the hang of the Nitty Gritty (cos there is a method IMO) I find that I get about 75% out with each combing session (so combing day 1 = 100 eggs, combing day 3 = 30 eggs, combing day 5 = 10 eggs....). So I am not surprised that you got about 100 first time and still 50 the next.
Don't forget that the eggs which the comb comes into contact with are destroyed - so some (many) of the 50 you pulled out today will probably be dead from yesterdays combing.
The trick is to try and comb the hair from different angles, so you catch the eggs that are on the top, bottom and sides of the hair shaft. My method is this (not sure it will make sense in words though).
Comb hair thoughroughly. Take a line of hair at the nape of the neck about 1.5-2" deep. Tie the rest up on top of the head with a clamp clip. Work from 1 ear to the other. Put the comb in close to teh scalp and lift it as you pull down the shaft so that the hair is horizontal. Hold this section as you get to teh end of the shaft. Then with the same block of hair put the comb in sideways close to the root and pull down to the end of the shaft. The repeat again putting comb downwards again.
Now move the comb along to the next block, overlapping it slightly with the first and repeart the 3 strokes.
When you have completed this layer let down another 1.2-2" of hair - and repeat.
It is dull. Just pity me when you are doing it. I have twins and it takes me about 2hrs by the time I have shampooed, conditioned combed and rinsed them both.