do I have perfect water?

I haven't tested my water in a while. Actually I only do a water change
once a month. I have a little bit of algae but not much. I just noticed
some red algae on the glass, which I did not have before, so I decided to do
a water test. Here are my results. Unless I am wrong, they seem very good.

Nitrate 0ppm
Ammonia 0ppm
pH 6.0
KH less than 53

I have a 10 gallon aquarium with 1 larger red cap oranda, 1 cherry barb, 6
small half clear light yellow fish, they almost look like they are in a
tetra family but I don't recall their name, I also have a pleco, and the one
apple snail which its health is questionable.

I have had all of these fish together for over 3 years. So, I am just now
wondering why the reddish algae when I have not done anything different over
these years.