I had the same thing with my jardini a few years back I came home found him on the bottom of the tank breathing heavily. I just did 20-25% and make sure the temp at around 80-82f and I add in some stress coat and a fe extra air pump. Then later that night i saw him moving around again. Normally I wouldn't recommend 50% water change unless u need to because a huge amount of water change in one time can stress out your fish. If u can I would recommend 20-25% a day for about 3-4 days