Methylene blue in breeder tank

[Ggz123]

I have a beautiful pair of Snakeskins in a 29 gallon bare bottom tank with large sponge filter. Ph is 6.9 and TDS is 70. There eggs always mold in the tank when they are left there. When I move the eggs and put them in a gallon jar with Methlune Blue they have an extremely high hatch rate. This is the only discus pair I have with this issue and all the water parameters and temp is the same in every tank. Should I add MB to their tank? If so how much? Thx in advance.

[CliffsDiscus]

I think the male is not always fertile.
If you think it's a tank problem switch the
spawn to another aquarium .

Cliff