TAP plastics
To determine you sump water height. With the pumps recirculating, fill the sump to find the minimum water level to where all of your equipment functions correctly. Mark this level, this is absolute minimum.
Next turn off the pumps and let the water level from the display find its level and settle into the sump. Fill the water level up to 1.5-2" below the top. Mark this point, this is absolute max. Or if lower, where you want the highest possible water level to be.
Depending on your rate of evaporation and dimensions of your sump, your water level will drop over the course of the day, if your lucky 2.....we are finding out the maximum duration between top offs without shifting the SG too much. Obviously the longer the better.
If your keeping softies and LPS you can let your SG fluctuate a little without any effects, SPS needs to be as tight as you can get it.
with a refractometer, fill the water to absolute max and set your SG at your desired level. (I set mine a little lower so as the water evaps, it doesn't go over NSW levels)
Based on what you keep, you can get a way with up to a 1ppm shift of SG. With a quality refractometer, let the water evap until it hits that point and mark it with a piece of tape, the top edge of the tape is "fill me" the bottom edge of the tape is "fill me now!!!"
If it gets down to your absolute min mark from earlier that is your tape line location, whichever you hit first.
Skimmer water heights..........they suck, you can make that your min and max heights in the sump as suggested by the skimmer manufacturer for proper operation and tape accordingly as before or if you want more water in your sump, place it on a stand or something in the sump to achieve the same underwater height. That way your skimmer selection now or if you get another in the future does not dictate your sump water level.
In the end, one of the benifits of a sump is increase water volume of the system, maximize that value.
Exit your display or skimmer exhausts under the water level to avoid noise, I don't know of any model related restrictions.
