I would say that is Ich aka whitespot.
You will need to treat the whole tank, but because Clown Loaches are sensitive to medication, wait for more advice (hopefully from Wilder)... It might be better to quarantine the loaches in a seperate redcued medication level tank, while running full dose on the main one.
Clown Loaches are very prone to Ich, the stress of just being a pair could be a factor here, if I was to ever get them I would have no less than 12 (enabling to form a complex hierachal structure). They come from warm (25C minimum) water with lots of flow (would be very happy with 20x water turnover per hour), in the hobby you are far better buying the right size tank for them once (a 6x2x2) but a higher capacity 4-footer like a Rio240 would suffice for a few years. "Marge" was well over 30cm (have a google)!
Your golden morph Chinese Algae Eater is another monster I'm afraid, could indeed be another stress factor, they reach ~40cm and have a nasty habit on latching onto the flanks of tankmates. Typically very spiteful fish as they mature, it begs belief why such fish are allowed to be sold in their hundreds of thousands each year around the globe to "innocent" fishkeepers.