Why is my neighbors pond so perfectly clear.

I have a 300 gallon preform. My neighbor has a 200 gallon preform. I do
have bio.mech filter and all she has is a simple pump with a canister
and one fine sponge in it. No bio balls, no course filter or medium,
just one fine filter that is tiny. She said she puts no chemicals in.
She has 7 6 inch fish which seems over kill. She said her secret is a
automatic fill and drain system. A valve opens and puts in tap water
everyday (15%) And the overflow tube waters her garden. She uses no
declor. Is it possible to do this? She has done this for 3 years and
never lost one fish. She has chorine in her tap water but says 15% daily
water change has not harmed her fish and her water is crystal clear. She
cleans the small canister filter and puts in a new sponge once a month.
Takes her 5 minutes. She does no other maintenence at all. Can A pond
function with no bio? Cause it seems great to me. I have never seen a
pond clearer than heres. And she feeds her fish 2 times a day and I
think to much but it works for her. What does everyone think about this
setup? Thank you