I have a 10 gallon tank that is about 2 weeks old i've been checking the water daily as well as temperature. I've done a few 10-25% water changes already over the last 2 weeks and have a betta, 2 panda cory's and 7 harlequin rasboras in the tank. In the last week 6 of the harlequins have died. Yesterday i noticed my betta was hiding in an ornament and would only come out to get a breath of air from the surface. When he did he would bolt up and bolt back down to hide. Upon removing the ornament it looks as if he has clamp fin. I don't know if you can see in the picture but it is sort of shiny on parts of him (velvet?). Also with the rasboras i notice their fin would start getting whitish as seen in one of the pictures. I don't know what to do now? I tested the water and ammonia is 0, nitrite is 0, nitrate is 5 and pH is about 7.6, also temperature is 78. Last week the water was a bit cloudy, probably due to over feeding due to flakes (i'm gonna use pellets now) but it is better now. Also i added the fluval biological enhancer to speed up the nitrogen cycle which appears to be developed now. If you have any suggestions on what might be going on and solutions please help.