Hi there lucky you. I love Tenerife and go there every year. You are so lucky that you actually live there!!!
Here is the thing, I dive in Tenerife myself and there is the question of summer time and winter time. And then there is the question of using a normal wetsuit or an open cell wetsuit.
You say you dive maximum 20 meters, but the waters at 20 meters can be quite a bit colder than the waters in 5 to 10 meters. You can use a "normal" wetsuit of 5 mm all year round, but properly not more than one hour in the winter.
However, if you use open cell wetsuit, you should use a "tailor-made" 5 mm wetsuit in the winter period, but then you can stay in the waters for hours and hours in my experience. However in the summer you can do just fine with 3 mm "tailor-made" wetsuit if it is an OPEN CELL wetsuit!!!
Forget about the 2,5 mm…. I don’t know how often you are diving, but if you only want ONE wetsuit and you want to dive all year round without worrying about getting could, you should buy a 5 mm OPEN CELL "tailor-made" wetsuit and on those few very hot summer days when the suit might feel a little to hot, you just open the suit a little and let some water get into it!
I have used a 7 mm "tailor-made" OPEN CELL in the SUMMER in Tenerife, and Oh Yeah it can be warm, because I use the same 7 mm in Denmark in the winter when the waters are like 3 to 5 degrees (and that is pretty cold my friend without a 7 mm "tailor-made" wetsuit), but once in a while I just let some water into the suit and I am fine.
That said, I DO NOT recommend using a 7 mm open cell wetsuit in Tenerife in the summer time unless you are a freaky crazy ******* like me.
So to sum it up shortly: A "tailor-made" 5 mm open cell is for you, you lucky ******* living all year round in beautiful gorgeous Tenerife, paradise on Earth in IMHO :t
