The best way to contact Sangtiennoi is via his Facebook here: https://www.facebook.com/sangtiennoi.sorrungroj
You can message him and his wife in English (simple English) or Thai.
(This website is run by a student of his and is only checked occasionally - so Facebook is the best option initially. Any questions regarding costs or bookings need to go directly to Sangtiennoi and his wife at the gym - Facebook.)
If you are having trouble getting in touch or have other questions please let me know below.