Fertilization fails

I have a pair of common ocellaris.  The female is consistently laying beautiful clutches of eggs now, and has been for about 3 months.  The pair is older, I got them from a local reefer and they had been breeding for him as well (though he didn't raise them).  They've recently restarted for me (in Nov.).  The first clutch was sparse (maybe 40 eggs, scattered around the clay pot).  
 
Since then she has been putting down a beautiful oval of tightly packed eggs about 2" by 1.5" on the clay pot.  She lays a clutch roughly every 11 days (12 days in a couple cases).  The first several clutches like this were fully fertilized, hatched, and I managed to kill them off in the larval tanks.  (usually at around 3 days or so).
 
The last 3 clutches have been laid down perfectly by the female, but then only a few eggs develop.  In particular, there are 400 or so eggs originally, but only 20 or so change colors as they develop.  The rest stay orange, and then are eaten by the parents.  Only the 20 make it to hatch day.
 
I take this as a lack of fertilization, is that accurate?  Any suggestions for causes?  Their diet was Thera A 4x daily, with a saturation feeding of mysis shrimp soaked in selcon 1x daily.  (this is the same diet I feed another pair that is currently more successful.)  The pair is fairly large (female must be 3" or larger, male is 2.5") and look great otherwise.  No diseases or medication for last year.
 
Thanks for any help.

Have you ever treated the fish for any diseases?

I haven't.  I can't say they haven't ever been treated, but at least not by me.  

Bump, could use any advice on the pair, even if its to separate and find new pairs.

 Bump, could use any comments, experiences of others, etc.  

Try different food?  Like a homemade frozen mash? 
 
You could try swapping the old male with a new male (preferably proven) the day after the last batch of eggs should hatch.  The new male may jump right in and spawn with the female on the old schedule.  It's definitely not guaranteed.  I wouldn't bother trying to trade out the female.  You could spend months waiting for a new nest that may or may not be viable.  Males are easier to replace than females because females take less time to mature.
 
I'm really just stabbing in the dark...

Don't let fear and common sense stop you! =]

Thanks for the suggestions, even stabs in the dark are most appreciated.
 
Changing the diet was one of my thoughts.  They are now eating TDO Oto C2.  I've also changed up the frozen, I do still feed them selcon soaked mysis shrimp at times, but also a home made blend that includes salmon, cod, shrimp, mussels, garlic and cuttlefish.  
 
They just laid a nest two days ago, and its been steadily disappearing ever since, e.g., not sure any eggs got fertilized as they are all disappearing.
 
Anyway, thanks for the suggestions, I'm going to give it another spawn or two and then try changing the male.

Good luck. 
 
Fwiw, when I first bought my very young breeding pair of Ocellaris the female was having troubles with her eggs not sticking to the tile when she laid them, and even though I saw a big difference about 3 months in, it took about 6 months of a new diet to straighten that problem out.

Don't let fear and common sense stop you! =]