The pair laid again and the fry are swimming about the tank now but they are slowly dying off.
Hello; First thing being you are well ahead by having parents who allow the fry to hatch and become free swimming. My pair always ate the eggs or wrigglers before they developed to the point of swimming free. There is some possibility your pair will become better parents over time.
You are correct that they are likely to spawn again. My pair did.
Could be a lack of food causing the die off of the fry but there are other possibilities come to mind. One thing I have seen is a loss of fry in general when raising these and other types of fish. I could speculate as to why a percentage of fry are not long lived but have noted some portion of them do not make it long.
Might even be a parent is picking one off every now and then. My guess being it is a struggle for them to fight the urge to take a bite sized fry. Just speculation on my part.
My first thinking to have quick food available for future spawns is to keep some sponge filters going in tanks somewhere. I have seen young fry grazing on the sponge a number of times.
I forget if you have other tanks available for this but do have an untested idea. I usually keep a few sponge bases stuck inside of a power filter. The purpose is to have beneficial bacteria (bb) loaded sponge filter bases on hand ready in case I need to set up a new tank quickly. Could be these sponges will also be loaded with tiny food stuff newly hatched fry can feed on.
(Note- probably wont help to have extra sponge filters in a tank where a pleco can get at them. I had a pleco who would feed on the sponge filter I kept in it's tank. )
Hello- one last thing comes to mind. I kept my spawning pair together all the time in a tank of their own. They would spawn every few weeks. It was too late when I noted the beating the male had taken from the female. He was game and took what the female dished out. He kept coming back to her and she beat him up pretty bad over time. They are cichlids after all. In hindsight I could have separated them and prevented his untimely demise. I guess the point is to take a good close look at both parents from time to time. Cichlids can play rough.