09-14-2011, 05:35 AM
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What are water stat's (ammonia,nitrites,nitrAtes)?
Considering mollies are fine, I might consider that over time,, with no fresh genetic's (new guppies) introduced ,prevention measures taken to reduce inbreeding, that strains weaken, and fish and offspring become weaker genetically and thus more susceptible to assorted pathogen's.
Is why it is often wise when purchasing fishes such as livebearer's to not purchase all of them from one tank.Iis Very good possibility that these fishes are all offspring from one or two adult's.
Better to introduce new males and females on occasion to prevent inbreeding which can weaken the strain.
Could also be that fish are simply reaching their expected lifespan and are becoming weaker.
Dietary needs can also influence overall health. Too much meaty foods and not enough vegetable or algae matter, and this can have negative effect over the long haul.(with live bearer's)
Must also look at water quality or lack thereof, along with possible addition of new fish that may have been harboring some bacterial pathogen.
Much to consider.