Greyish spot on my gourami pupil

[fishmadpete]

Not a real emergency, now, but I have had several deaths recently without any real signs of cause. The tank readings were all ok with nitrite being 0 and nitrate being around 20.
I have looked through several books trying to work out what was killing my fish and the only thing I have come up with is fish TB. My angel exihibited classic symptoms with being very lethargic, off its food and sitting on the bottom of the tank his eyes had a grayish cloudiness. He died within 24 hours. I had recently introduced some new fish that have also died. Unfortunately at the same time as introducing the new fish I added yet another filter this caused more current which may have caused more stress on the fish.
Any way the deaths have stopped since doing a partial water change and adding some tonic salt to the tank.

However I have noticed that one of my indian gouramies has a grayish coloured spot in the centre of its left eye. It would also appear to be blind on this side as I can aprroach him on this side without him swimming off. If I approach from the right side he swims away. Does anyone know what this spot could be. The books say that TB can effect the eye by making it "pop" could it also cause the spot??

The tank is approximately 150 uk gallons and now houses
1 x medium plec
1 x red finned loach (medium size)
1 x medium kissing gourami
2 x indian gourami
1 x pardise fish
4 x Bronze coris

It use to contain
1 x angel
5 x lemon tetras
5 x neons
5 x red nose tetras

any answers to the gourami question gratefully received

 

[gadazobe]

Sorry to hear about the deaths, but one thing bothers me. You say that the deaths stopped after a partial water change and that makes me think that the problem is with the water. How often do you do water changes and clean the gravel? Have you checked for ammonia. Even if your water parameters are good, there are still background pathagens lurking in all tanks and these are just waiting for an opportunity to attack the fish. Regular water changes keep background dangers in check.

 

[fishmadpete]

I usually do partial water changes once every two weeks which seems to have been ok for the past twenty years. The tank has been going for the last two years like this. Partial changes include gravel cleaning. To be honest I haven't check the ammonia levels. PH is about 6.5 - 7.0