Thanks for all of your support and ideas, they are much appreciated. I will see if I can find a photo of my tank, I know that I have a photo of the original set up but since it has been renovated they have more room now (about 10L each).
I can't really use a knife to scrape out the silicone without completely dismantling the tank because of course it is the silicone that holds it all together but I will definitely be soaking and rinsing the tank several times.
I have heard a lot of good things about the craft mesh and was thinking of using that until I read a couple of negative feedbacks on it where people have had pretty much the same thing that has happened to my fish happen only with the craft mesh instead of the fly screen...... maybe you can buy different brands of craft mesh and maybe some are safe and some are not?
I went to my petshop yesterday and searched for the plastic dividers for tanks but they were so expensive! It would have cost me $150 just to divide my tank and I can't afford that but I found these netting filter media bags and I bought them and are going to use the mesh as dividers instead of the fly screen.
MSG I had no idea that the softer meshes contained chemicals such as those you mentioned! I have learnt a valuable lesson and will never put anything that is not especially designed for aquariums in any of my tanks again.... ever!!!!
I can give everyone some good news though, little Eclipse is now 100% recovered and Secret and Berry have improved greatly, I can quite confidently say that I think they are all going to recover just fine, they have started eating again and are getting more active so things are defiantly looking up for my little guys and guess what I bought another betta yesterday, he is a halfmoon butterfly with a deep royal blue body, so pretty but his tail was pretty tattered when I got him and there were other sick bettas in the shop so he is being kept away from the others ATM. I hope his tail improves, I do not know if he has fin rott, flukes or has been in a fight with another betta because he is also missing some scales. I will post some pics of him as soon as I get some he is so beautiful and I need to name him too.
Thankyou again for all of the support and advice