Hello, this is my first post, I am a complete novice I'm afraid. I bought my new Jewel Vision 180 litres about 3 weeks ago. After cleaning the gravel and filling the tank I added the water conditioner, set the temprature to 26.79 and put the caves and objects in. After 1 week I added about 20 Guppies, they were fine so a few days later I added a Albino Rainbow shark, silver shark, two clown loaches and a sucker catfish pleco. Again one week later they were again thriving and getting along fine, I then completed my tank by adding 8 tetra, two platties and one male beta. I also added 1 live plant and 1 plastic plant covering the filter. This is where my problems have started, 4 of my 8 tetra have died, one of them within a few hours the others within 2 days, I don't think the other will have long either. All my other fish seem fine though except for my male Beta who is acting really wierd, he is either just still looking dead by the filter at the top or hiding at the bottom, he does sometimes swim around but his tail and other bits seem very droopy and his body seems to be losing colour. I have just ordered a Ammonia test kit and digital Ph reader to test the water although I feel it may be ammonia levels. I think I may of rushed and introduced to many fish to soon and am now worried about the other fish I have although they seem ok at the moment. Any help from yoiu experts will be appreciated as I would like to help the beta. I will do a 25% water change tomorrow to see if that helps.