I was rethinking what I wrote and why don't you just borrow a skimmer from a friend and see if it works? Your skimmer sounds like its pretty finicky. Whats the brand and model?
The Skimmer is a EuroReef. It may be a bit too much for this 65 Gallon. However it will take the me long run once more load happens over time. Better to be BIT over, than under.
I actually have two (one in each tank), and as I mentioned I switched them around and the problem is related only to this tank. So changing skimmer is not the solution. I need to find the cause and resolve it. (I think I'm close).
Actually I like this skimmer, and the fact that it's
finicky, which I would call
sensitive is a GOOD THING.
Why is SENSITIVE good? We'll let's say you don't properly rinse you hands after handling soap, paint, or oil etc. This skimmer would quickly point this out, if I put my contaminated hands in the water. It's happened to me. A in-sensitive skimmer would allow you to continue to pollute your tank with your soapy hands. Bad thing for a SPS tank over time. (any tank for that matter)
It's reaction (over skim), means it's picking up some foreign substance and getting it out quickly, or reacting to a change in steady-state-water-condition. Nothing wrong with that. Actually Very good.
A crappy skimmer in this situation would continue to run happy, and not point out this issue.
So I'm not looking to find a skimmer that will ignore this problem in this tank.
I actually did buy a skimmer (won't name brand) a few years ago. It took forever to skim a 1/8 of a cup. I then put this EuroReef in parallel and it skimmer a 1/4 DARK cup in a couple of day, while other barely got a film started. That skimmer is running my Quarentine, Holding tank. (Useless. I use it for water aeration).
Till now I've been playing around, here and there. But I will take a bit more systematic approach, when I have a bit more time, and find the root cause.
At this point my last adjustment to lower the sump water to lowest possible appears to be a bit better. 1/4 cup of wet skim over last night. (Not clear skim, but a bit yellow/green).
My next little experiment, is I'm going to run the TOP UP hose to my overflow box. That way the pure RO water will get mixed up, before reaching the sump. I'm also going to reduce the hose at the end, to trickle in the top up water.
Still, I don't want to mute the problem, if there is something foreign going into tank.
If it's just a overreaction to Clean RO water caused salinity changes. Fine. (but it can't be, since a gallon of RO water dumped in, does nothing).