Thanks for your quick reply! I think I'll just do the water changes and keep an eye on the other fish. I didn't rush to clear out the mela-fix and pima-fix as it recommends it for adding new fish, so I figured it could gradually come out during water changes and that would help to prevent it from being spread to the other fish.
They do all seem to be acting normally, they rise to eat and swim around like normal. Buddy has gone back to rooting out bits for himself and the others, he really does go all over the tank. I am also going to wait a bit, then get 2 more pandas, I had wanted 6 originally but am not wanting to overstock the tank because of it's size. Then I will have 1 betta, 5 harlies, 5 pandas and 2 otos and tons of plants.
Now the CO2 bug has bit me well and truly, I haven't got the unit for the 25 and I'm already making inquiries into a DIY for the 10! The plants are looking good, but I think they could do better, the trick seems to be keeping iron and potassium going into the tank, CO2 would also lower the KH and pH a bit, then I wouldn't have to use quite as much peat as I do, not that I will stop using the peat, I love how it makes the fish look! And it is also supposed to make them more immune to fungus. I'm sure you were right and the betta tore his fin prior to me turning the filter down, that would allow the fungas to get in. The panda's have been doing some flashing before the water change and the one that died could have been wounded doing that.