Iron removal filter in an apartment complex in Kumbakonam, Tamil Nadu - Need pro's & con's

I live in an apartment complex in a village near Kumbakonam, Tamil Nadu. Our borewell water has 3.1 mg/ltr iron.
Since we (the apartment owners) did not arrive at consensus on installing iron removal filter, About 1 year back, I installed an iron removal filter specifically to my flat. I have a separate sintex storage tank. I tested the filtered water and it did not contain any iron.

But 2 months back, the builder had agreed and installed an iron removal filter catering to all the flats. But the test shows that the filtered water has 0.16 mg/ltr of iron.  I am continuing to use my own iron removal filter also. ie the output from the main filter is given as an input to my own filter and the filtered water gets stored into my own sintex tank.

My questions:
(1) Is it proper to use an Iron removal filter when the water has very little amount of iron (0.16 mg/ltr in this case)?
(2)Since the maximum iron is filtered at the 1st stage (I could see the complete redness in the backwashed water), I could see no redness during the backwashing of my filter. But the backwash water's colour is black. The resin used is  black in colour. Now I am worried whether the resin's life will come down drastically due to this type of use.

Please advice on best course of action possible.

R Balaji