Mysterious Deaths...

[bluesword23516]

So over the past 3 weeks i have had two guppies die. One was male, the other female. I haven't added anything new and the tank is cycled and has no out of the ordinary spikes in readings.  Any ideas? They are probably 6-8 months old, both at breeding age.  The male I saw the day before looking a little sluggish at the top and not really interested in food. The female I just found when I got home today. Both of their stomachs were eaten out, but I have seen that before, the fish just tend to eat it because it is accessible. 

 

[bluesword23516]

I actually did add some rocks into my tank a while ago. But it hasn't done anything to the tank and I rinsed them really well multiple times so any chemicals should be long gone. 

 

[Byron]

It will help us if you can post a bit more data.  How long has this tank been running?  What size is it? What fish are in it?  Water change schedule? Any substances going in the water? Water parameters (GH, pH, temperature)?  Have you tested ammonia, nitrite or nitrate and if yes, what were the results?
 
Lots of questions I know, but a fish death can be due to many things, individual or combined.
 
One quick comment on the rock, while not at all suggesting this is the issue; rocks absorb liquids and these can leech ouit over years, so no cleaning can possibly get them out if they are there.  Again, not suggesting there is any issue with the rock, only pointing out something for you.  Wood is the same, by the way.
 
Byron.