Maybe columnaris???

Symptoms:

White spots on mouth, edges of scales, and fins
Cottony growth that eats away at the mouth
Fins disintegrate beginning at the edges
'Saddleback' lesion near the dorsal fin
Fungus often invades the affected skin
Rapid gilling in cases where gills are infected

Most Columnaris infections are external, and present first as white or grayish white spots on the head, and around the fins or gills. The lesions may first be seen only as a paler area that lacks the normal shiny appearance. As the lesion progresses it may become yellowish or brownish in color and the area around it may be tinged red.


Lesions on the back often extend down the sides, giving the appearance of a saddle. On the mouth the lesions may look moldy or cottony, and the mouth will become eaten away. Fins will erode and have a frayed appearance as the infection progresses. The gills filaments will disintegrate as the bacteria invade them, and the fish will begin breathing rapidly due to lack of oxygen. Less commonly, the infection will be internal, and display no external symptoms.

Treatment:

Change water
Vacuum gravel
Add aquarium salt
Treat with copper sulfate or antibiotic
Discontinue carbon filtration during treatment

External infections should be treated with antibiotics or chemicals in the water. Copper sulfate, Acriflavine, Furan, and Terramycin may all be used externally to treat Columnaris. Terramycin has proven to be quite effective both as a bath, and when used to treat foods for internal infections. Salt may be added to the water to enhance gill function. Livebearers in particular will benefit from the addition of salt, however use caution when treating catfish, as many are sensitive to salt.

Prevention:

Quarantine new fish for two weeks
Maintain high water quality
Provide fish with a nutritionally balanced diet
Medicate fish prophylactically before moving them
Disinfect nets and other equipment before using

Because the bacteria thrive on organic wastes, it can be controlled by regular water changes and vacuuming of the gravel. Proper diet and maintaining good water quality in general will keep the fish from being stressed and therefore susceptible to infection. To avoid spreading the bacterium, nets, specimen containers, and other aquarium equipment should be disinfected before each use. Small quantities of aquarium salt can be used to prevent disease in livebearer aquariums. When fish are being shipped or moved, they may be treated prophylactically with antibiotics or by feeding them medicated food.

Difference in pH of 6.8 to 8.8 is 100 fold in chemistry term which I find very extreme condition for majority of f/w fish.
I've done many experiments with fish as to adaptability in refrerence to pH but not that high for type of fish which are found in the opposite side of pH scale.

I dont know if pH was this high from the beginning but my assumption is that pH may have increased recently thus began experiencing problem. Again, you should be the one who should compare pH reading since the beginning.

Before doing any changes or treatment, how about double checking your pH of tank water and tap water?