I'd try the slower eggs at higher temp. 8-10 weeks seems excessive.

I had a similar problem with my gardneri species. It was not just one species , but all of them. (5 species)Eggs just remained clear for months, with no visible development, I tried everything imaginable like temperatures and water makeup and nothing helped. This went on for over a year. I finally with great difficulty dumped all of my gardneri. Many fish went down the drain. I purchased a couple of new gardneri species to see if I still had the problem. The new fish were  kept in the same conditions as the old fish and laid eggs that developed and hatched in 14 days just like they are supposed to. Still have no clue as to why my  old gardneri fish had such a problem.