Seachem Excel can be toxic if over dosed if you have add more then the recommend amount that could be the cause of the symptoms your seeing I can't say for sure that the cause if it is suffering from swim bladder you want to do Epsom salt baths 1 table spoon for 1 gallon for no more than 15 minutes for 5 days as Epsom salt acts as a muscle relaxant to help relieve pressure on the swim bladder @Zesul