Calcium/Trace Buildup?

[Sampo]

Hey peeps, i have a 55g rimless. Over the past few months i've started to get a water line.

Seems just like trace elements. Also my skimmer had been acting up, took it apart and it had the same buildup inside the mag chamber of the pump and on the air intake. The tank has only been up and running for a few months

Im not dosing anything right now, maintain levels mainly by weekely water changes.

Am i doing something wrong here, any ideas?

Thanks!

 

[Reef Breeders Verified Sponsor]

Might be low magnesium causing ca and alk to precipitate, could also be just saltwater splashing the tank.