What are effects of not changin water for long periods?

I havent had time to change water in about 5-6 weeks due to some work and
family related issues. Took time to add treated water though. There seems to
be no ill effects and the water readings are pretty good and consistent with
the exception of the water being a little hard. The water is becoming
somewhat cloudy. What are some of the problems I might come across with not
changing water for long periods?

20 gal. tank
Clown Loaches
1 Pleco
3 Black Molly
2 Swords
4 tetras.

1 real plant (Cant remember what its called but its long and thin and grows
very rapidly)

Thanks
J