Random rasbora and glowlight death...

[branwitch]

I have a standard 55g that has been set up for a few months now.. i had 8 espei rasboras, 2 german rams, 2 platys, and a lepord pleco all bought randomly throughout the first month. There is plenty of airation, two foam filters going, one topfin 40 filter running on ammo-carb, and one other high volume filter running on pure ammo chips. i have an exess of hiding places and an exxess of live plants, mostly java moss and anubais, and still a lot of fee swimming space.. so recently i bought 6 harlequin rasboras, and 5 glow light tetras... for about a week everyone looked fine, ate fine, and acted fine, then one morning i woke up to a dead glow light and a dead harlequin.. no body damage, no diseases. this kept happening, about every 2 or 3 days i would find 2 or 3 dead rasboras and/or glowlights... it has been happening for about two weeks now, the last time being yesterday loosing one espei. The rams are doing fine, actually breeding, and the platys and pleco are doing fine also.... i have been doing about 25% water changes every two weeks... and my pH is a solid 6.5, GH is 60ppm, no nitrites or amonia, and very small traces of nitrates.. and the temperature stays at a solid 78F-26C. im just wondering if anyone has had this happen, or could guess at what it is... because its completly beyond me why only rasboras and glowlights are dying, and they are dying so spuraticly...

thanks - branwitch