With so little information it is hard to make a diagnosis.
How many of each were in the tank? Each of the fish mentioned are schooling fish and prefer large numbers. Never do well singly or in pairs.
How big is the tank? How many fish in it, what filtration?
Did you do a water change? What is your water change schedule?
Did you clean the filter out prior to the die off?
Was there any cloudiness to the water?
How long has the tank been established?
What is the pH and hardness?
Planted or not?
Were the fish showing unusual behaviour? Gasping, swimming near the surface, flicking against things? Lethargy?
And many other questions, but these will do to go on with. I know what I am thinking, but without these answers cannot help much further than to say, probably ammonia.
Hello Andy, sorry for the my absence. Yes, the PH was way to high at 8.5 All sorted now, Thank you so much
With the pH that high, ammonia would have been really toxic even in small amounts! Not to mention all of those fish like it acidic, 6.5 - 7ish.
Sorry you had this experience, do not be discouraged though, we all lose fish from time to time. I lost some rainbows a few weeks back when it was stinking hot and the pump went down.
Thank you so much for the encouragement. The ph is stubbornly remaining at 8, I am thinking of replacing the lifebearers with African Chiclets. Apparently they quite like more alkaline water. Any advice would be appreciated
Sympathies with the loss of your rainbows.
The first thing to ask is what is the gravel substrate in the tank, the next is to ask the tank decor (rock, ornaments etc). Something is obviously buffering the pH and hardness in the tank to remain that high. Calcium and magnesium carbonate are the 2 primary contenders, so any coral, limestone, etc is immediately out, as are many other rocks.
next question is, what is the pH and hardness of the water going into the tank.
Be aware that African Cichlids do well in alkaline water, with a high pH, but some of them are very aggressive (well, pretty much all except the leptosoma are aggressive.) If you want something a little more calm than they are, Guppies, Swordtails, Mollies, Platies and other live bearers do very well in a high pH and hardness. Just make sure there is plenty of Java Moss for the babies to hide in.