Help!Redtail shark disstressed!

My redtail shark was fine this morning but is now swimming listlesly in a vertical postion, all other fish in the tank are acting fine at this time. I did a 30% water change two days ago,and since finding the shark like this checked my chemical levels which are nitrate 40,nitrite 0, alk.180, Ph 8.4, the chlorine level is safe also, after checking the levels I have done a 15% water change and added a dechlorinater, what else can I do? I have not added any other chemicals or meds to this tank for quite some time,I have no live plants but I do have an air stone going.

no typo, according to my test kit it reads 40 which is at the high end for safe levels, the same for the ammonia test. for tank mates I have mollies,platies,swordfish,and one each glass catfish,betta,and pleco. the red tail seems to be doing better at this time he is hiding in of the thecaves I have in the tank,still worried though:shake:

thanks for the input,perhaps the water changes helped,plus I lowered the ph,he is acting much better then earlier today,will continue with more partial water changes also.