If you are not getting many discus fry from your discus breeding pair spawns, then try some of these tips below to hopefully help maximize your discus spawn yields.
Lower Water Hardness in Breeder Tank- This is probably the first tip to try if your discus spawns are having terrible hatch rates. Having hard water in your discus breeding aquarium will cause the shell of the newly laid discus eggs to harden quickly. This makes it very difficult for the male discus to fertilize these eggs. Try lowering your water hardness to around 100 to 200 microsiemens. The softer water should give the male plenty of time to fertilize the spawn.
Keep Breeder Tank Super Clean - It's important to keep your breeder aquarium very clean. Wipe down all the sides and surfaces when doing a water change. Try to do at least two 25% water changes during the week. Clean water will reduce the chances of bad bacteria or fungus killing your discus spawn. Keep your filters clean as well.
Use a Diatom Filter - A diatom filter will help super clean your breeder tank. Diatomaceous earth filters can filter the water down to 1 micron. They'll even remove parasites, like gill flukes, that are a common killer of small discus fry. The best time to use the diatom filter is right after you've cleaned the breeder tank and did a water change. You only need to run the diatomaceous earth filter for a few hours.
Clean all Spawning Surfaces - It's important to keep the discus fish spawning surfaces clean in your breeder aquarium. Clean all spawning slates, bricks, cones or PVC pipes in your aquarium at least twice a week.
Add Methylene Blue - Adding Methylene Blue to your discus breeding tank after they've finished spawning will help protect the eggs from bacteria and fungus. Just remember that methylene blue will probably stain the silicon seals in your glass aquarium.
Protect Spawn with Wire Mesh - Many large spawns are lost because the pair will eat the eggs or wrigglers. Try putting a stainless steel wire mesh around the spawn so the pair can still take care of the eggs and wrigglers, but will be unable to eat them.
Remove the Bad Discus Parent - Many times it's only one mate of the discus breeding pair that has an appetite for eggs or wrigglers. Monitor a spawn to see which one is eating the eggs and remove it from the breeding tank. Don't leave the baby fry with the lone parent for a long time, especially if it's a large spawn. Start feeding baby brine shrimp 2 days after the fry are free swimming.
Use Surrogate Discus Parents - If you have a pair that constantly eats it's spawn, you might want to remove the eggs and put them in a tank with another discus pair that also has a spawn. With luck, the other pair will take care of the 2nd spawn as its own.
Treat Pair For Gill Flukes - If your discus fry starts dying when they are pea size, they probably have gill flukes. Treat the discus breeding tank for gill flukes.
Stop Water Flow Near Spawn Area- If your pairs are in a central system, you might want to reduce or even stop water flow from entering the breeding aquarium while the discus pairs are spawning. Strong water current can flush the sperm away from the eggs causing them to remain unfertile.
Filters or airstones near a spawn can also cause the water flow to flush away the male's sperm from the spawn. Move the filters or airstones away from pair while they are spawning. You might even want to turn off the filter while they are spawning. Just remember to turn it back on after the discus pair has finished spawning(usually less than 45 minutes).
Try Using Another Male Discus - Unfortunately, many male discus are not as fertile as their owners would like them to be. Some causes might be from too much inbreeding or hormones given to them to enhance color when they were young. If your discus pair has spawned many times with very few eggs ever becoming fertile, you probably should replace the male discus with another fish. If it's a young pair, you might want to give them more time. A young male discus might need many spawns before he gets the fertilization process right. Breeding discus takes patience.
Artificially Raise the Spawn - If both discus fish parents are egg eaters, wriggler eaters and free swimming fry eaters, then you just might have to take the eggs away from them and artificially raise the discus spawn yourself.