A stupid question regarding protein skimmer
 

I run a rio protein skimmer and it is collecting good amount of "brownish" water in the cup. I was just wondering, the water that protein skimmers collect, is it just liquid waste or water from the tank with the junk? I do have to top-off with fresh water every 4/5 days due to evaporation but would also like to know whether skimmers removes some saltwater too.

Your skimmer will remove a small amount of salt. The amount is dependant on how wet/dry you're skimming, but in either case it's pretty much negligible.

So its actually very small amount of "saltwater" and mostly junk? Like, if I get a cup of brownish water, I don't always have to replace the tank with a cup of saltwater to maintain the same water level right?

No, you don't have to replace the skimmate with new water.

Thanks :D

Actually I am running a rio nano skimmer in my 20 long and its sucking up good amount of junk esp after adding few frags of softies (good that it has a big cup compared to some other HOBs) so thought whether or not I need to replace the same amount of water with saltwater.

Just check your salinity. If you find the salinity has gone up by 0.001 add some freshwater. Make sure you are using a hydrometer that has been manually calibrated or a refractometer that you calibrated a few times per year.

Yah I do that :D

BTW did you refer "manual calibration of hydrometer" as checking the reading with freshwater?

No, that is not a good way to do it. A hydrometer should be checked against a calibrated refractometer. If you don't have a refractometer your LFS should be able to check your hydrometer against their own refractometer. Just politely ask when they last calibrated their refractometer before using it to calibrate your hydrometer.

Ooooo...yah that's a good idea....but hopefully in sept I will be buying a refrac...they are pretty cheap in ebay :D

Yeah, you get what you pay for though. Sometimes you're better off looking for a better brand in the used classifieds. :)