Hi and welcome to the forum
What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
What type of plecos were you interested in?
There are a lot of them and some are small but others get way too big for an aquarium.
Hi welcome to the forum

if you are after a pleco tank pick something small like a Bristlenose or Bulldogs and set up a group - possibly able to breed them. Or if you wanted to go for something fancier things like Leopard Frogs or Flash Plecos, Blue Panaques are very nice too (would probably be top of my list).
You may want to keep a small school of tetras with them too, maybe something simple like Ember of Green Neons, too small to be a risk to any young or eggs but schooling to provide a bit of confidence to the plecos. Sometimes fish kept without smaller fish get stressed and hide more as they assume there is something near by eating the small fish.
Wills
Hi, yep I have seen a blue panaque , very nice, good idea about tetras