Hmm, you didnt change like lights or move the light, or put the frogspawn through more flow than normal? When adding the new water how did you add it to the tank??? If you just dumped it in to the main tank, with out matching the temp to that of the tank, and giving the frogspawn more flow, that could cause it... I would also try to stay away from doing a 30 percent water change, Do smaller one more frequently. .5 gallon would be suffice weekly.. GL hope he gets better.