worried about my fish

[vantgE]

yesterday I did a large 50% water change in my 90 gallon tank most of the water added back into the tank was cold water and the tempature went way down. But I was able to move it up within half an hour to a safe level then higher the rest of the day. But all my fish had been acting wierd just sitting around and barely moveing, not eating(huh? their always hungry) now they are better slightly more active and improved apetite, but still not at their best. I found a dead fish a few days ago dead for unknown reasons he had been eaten at, before or after death I am unsure of. Now I have a fish staying mostly at the top of the water with her head down and her tail prettyt much out. I tried chaseing her away from there and she returns. What could be wrong I have no idea why the other fish died or this one is acting as such please help.
The tank is 90 gallons
Nitrate, Nitrite, and amonia are fine, 0 0 0 Recent large water change (possible cause)

Ph. between 7.5 and 8, But one test was off the charts much above 9.5 after I changed, but I have retested twice to get 7.5 between 8.0

1 male 3.5 inches maylandia lombardoi
1 4 inch nimbochro, is venustus
3 (or two dead fish unidentified one of these is acting bad) 2 inch maylandia lombardoi
7 (or six) 1.5-2 inch pseodotropheus elongatus
7 2 to 3 inch melanchromis johanni

I'm thinking it is either agresion from the male lombardoi or something from the
water change

Thankyou

 

[tstenback]

Could be temperature shock. How big of a temp difference when you did the water change?