Started cycling my 65g on 10/4 (last Tuesday), so today is Day 6.
Sometime this morning I noticed a "mystery" foam appearing in the filter sock that captures the water from the tank return into the sum (see 2 still photos): looks just like soap suds. BUT, nothing was washed or rinsed in soap.
I removed the sock and rinsed in tap water followed by a RO
rinse (I'm waiting for socks to arrive or would have used a new one). During the rinse, nothing seem abnormal. Placed the sock back on the return line and the foaming action continued.
To me (through novice eyes) it appears like what I would expect from a protein skimmer (based on the numerous videos I've seen).
The greenish tint shows up more in the photos but water is slightly green tinted - I assume an algae bloom starting.
Here are the numbers I've tested today - same as yesterday, save that the nitrates are showing an increase:
Salinity (with refractometer): 1.026
Ammonia: 1 ppm
Nitrite: 2 ppm
Nitrate: 10 ppm