Yes I do know my water parameters.0 ammonia 0 nitrite 20-40 nitrates.
Ph-7.5-7.6(hard to read on the API test)
Also I looked up the maximum size of bolivian ram which is 3 inches I believe?I don't know if they are very active or not so that is why I am asking if it would be alright.
They are active, and hold quite large territories in the wild, so would in no way be suitable for a tank of that size.
Really your only options for a 5g are a betta, shrimps, three or four male Endlers or guppies, or a small shoal of six 'micro' fish, like ember tetras or CPD; but they tend to be very nervous kept in small numbers, so you would have to have the tank very heavily planted and, even then, you might not see them much.
Limescale?Im guessing you mean a dust like residue that is white?Not much,we get a small amount of that stuff.I thought of going with maybe 3-4 guppies?
I agree with others that a 5g is not sufficient space except for a single Betta, or a small group of the "nano" fish like Endlers (if moderately hard water) or the micro rasbora or similar if soft water.
On the water hardness, check with your water authority, on their website you may find the water data that includes general or total hardness, and carbonate hardness or Alkalinity is also worth knowing.
If you post the link, I can take a look, sometimes they hide this rather well. Or, you can call them. You want the general or total hardness, and you want the carbonate hardness which is sometimes called Alkalinity. With the number, make sure you get the units they use to measure, like mg/liter, or ppm, or degrees, etc.
That is one of those data sheets concerned only with bad things in the water (nothing there is a problem for fish) but no mention of GH/KH/pH. You will have to call them.
The very low basically zero nitrate/nitrite is good; not everyone is blessed with this.