Albino half dark belly issue

[GundamCichlid]

Hi

I have lost couple 4-5cm albino longfin and shortfin with the belly of them is become dark.

there other that left are 1 male 11cm and 3 female 7-8cm and 3 fish 4-5cm

They are in 90L tank, 60x36x 45 m with sponge filter and half liter matrix scatter in the bottom and bare bottom

Water parameter is fine an the adult seem ok and eating

Anyone had experience this before and what might be the cause and the best solution or prevention please share

Panic mode "ON"

Thanks

[YAL05T]

I have seen ABN get what look like burns for want of a better word when kept in a high ph. What are the actual water parameters and what are you feeding them?