Forgot to mention that we have about an inch of rocks - not too many.
Images:
https://flic.kr/p/pthC2g
https://flic.kr/p/prfyYE
---------- Post added at 05:04 PM ---------- Previous post was at 04:56 PM ----------
I think the first picture is most indicative of what it looks like. We have a lot of plastic plants and an inch or so of rocks, so that would give the good bacteria places to thrive.
As far as iron-rich, we're not too bad. We do not have any iron spots in the toilets or sinks in the house.
We have a tank light, but it is LED if that makes any difference. It's in a spot of the counter between windows so we keep the lights on - otherwise, it almost looks like nighttime in there.