@Calmwaters
+5 cents, since they don't make pennies any longer.
A skimmer will remove SOME dissolved organics (DOC) so it can be useful if you tend to overfeed. It will slightly lower nitrates and phosphates due to the removal of the DOCs. It will also reduce some essential and trace elements. It has been a very popular device since the late 70s but it is never essential unless you design your filtration strategy around it. Most of your filtration happens in your rock and sand.
Where a skimmer is most useful is to increase gas exchange. That increases oxygen in the tank and, assuming the CO2 in your home is on the low side, will increase the pH of your tank.
It, like almost every piece of equipment on your tank is a trade off. It helps in some ways and hurts in others.
I do run a skimmer on my current tank but it is intentionally undersize and I run it fairly dry as I don't like stripping elements and nutrients just to spend more money reintroducing them. I use it mainly for additional gas exchange. My CO2 levels are pretty high since we are always home so it doesn't really help our pH at all.
