I've never heard that about the oxygen in the water before - I'm learning something new every day! I'll be sure to take this advice on board for my water changes in the future. For example, I use 5L bottles to store my new water in for about 24 hours before a change but I always close the lid, I should really be leaving it off right?
Sorry if this classes as a threadjack!
No not at all

Fishy is looking a little better now hes swimming with his pals again . maybe not as straight as id like but hes improved greatly and they aren't gasping anymore so all good so far thanks everyone .