The temp and salt are a good start. It sounds like your poly is running a bout of bloat. It's not certain what the exact trigger is that causes this. But, it seems to occur with infrequent water changes, lower temps, and undiverse feeding regimens.
There's a product called Metronidazole. Use of this med along with the salt addition and frequent water changes have been successful in beating bloat.
Perform at least a 30% water change, treat with the med, and don't try to feed the poly for the next several days. On day 3 of the treatment, perform another water change and retreat with the med at full strength. Repeat this plan for a third treatment. During the treatment, watch your poly for waste elimination (sign of kidney function) and check your ammonia level. As the poly kicks the bloat, it'll dump a huge amount of waste to clear its system so, additional smaller water changes may be needed to keep ammonia levels down. A couple of days after the 3rd treatment, you can offer your ornate some food. Increasing plant protein in its diet will help in flushing its system and can be achieved by stuffing algae wafers or spirulina into non-living food or by gut-loading live food items prior to feeding them to the ornate.
Once the bloat is long over, keep up a regular schedule of water changes. Continue to offer foods that contain animal and plant protein (gut-loading is the easiest way). I also recommend keeping a trace amount of rift lake salts in all poly tanks to help maintain proper kidney function and osmotic regulation. Rift lake salts differ from sea salt in that rift lake salts are a calcium chloride derived salt instead of sodium chloride derived salts from marine mixes.
I maintain close to 40 polys and have followed this plan since my last bout of bloat over 8 years ago with no reoccurrances of this disease. Good Luck.