Remora HOB skimmer filling with water

[425nm]

I just set up a Remora skimmer (bought used with a maxijet 1200) and the collection cup has been filling with water about every 45minutes.
As I understand it there is a "break-in period" but at the rate the cup is filling I can't leave the thing unattended for fear of a flood. I've got the cup pushed up all the way. I pulled the manual online and it mentions that water conditioner could cause such foam. I'm stuck using tap water (too poor for RO/DI). I've been using aquaplus. Are there any conditioners that don't cause this?
On a related note, could Aquaplus potentially cause problems in a reef tank since the active compound is EDTA which also chelates Mg2+?