Male died whilst on eggs?????

[FishyMcFishFish]

Upon returning home today I noticed that my male calico bristlenose was on his back at the back of the tank behind a large amazon sword, dead. I had raised him since about an inch and he made it to just under 4. he was in his second tank (from a 64l to a 120l) and had 4 batches of fry with his female (two batches in each tank). The problem is, he had been guarding a 5th batch in his new slate cave. They are still eggs, no fry have hatched out. since I don't own an egg tumbler I have created a contraption involving a fry trap and some airline. Will This do? I will try to attach a photo.

I do weekly water changes of around 20-25%. the current water values are: pH 7.2, ammonia 0.2ppm, nitrite 0ppm and nitrate 10ppm. I have changed the substrate recently (about 2 weeks ago) as the old substrate (a mixture of sand with a grain size larger than small gravel and plant substrate) somehow had baby pleco poo infused into it so that whenever the adults moved they created poo clouds. I also added 3 massive sponge filters to go with the big canister filter that they already had. I plan to remove the canister filter at some point over the next couple of weeks. I believe that the climb in ammonia and nitrate could be down to the change in substrate and the previous water quality. However, I still don't know why my prized male passed away, especially at such a critical time.

[SLIMESLAYER10]

were the spawning's back to back? if so the male could have been starved. they don't eat while they mate or while there on eggs so they can go for 3 weeks without eating. if they do this more than once without 2-3 weeks of recovery they can die.