Hello. I put 6 in my 29 gal. on Sat. to go along with 1 blue gourami and 2 spotted cory. Within 24 hrs some developed symptoms much like shimmy? They are shaking but are not swimming around. One died yesterday and I believe others will also because they are showing the same symptoms. They have no appetite. I tested my water on Sat. Ph 7.4 Amm 0 Nitrite 0 Nitrate 10. Water temp 78. My tank is approximately 3 months old. I do partial water changes(25%) weekly. I have plastic plants only. Any suggestions?