When my 2 biggest clown loaches (8 total) started doing this I searched and most answers consisted of the person must be mistaking their loaches playful behavior as fighting. A while back I found information about clown loaches fighting for dominance. There was an illustration of the loach 'graying out' - exactly what my loaches do. They will face each other , lip lock get into a frenzied squabble like a couple of flowerhorns! Usually occurs right after or during a feeding. Will go on for 3-5 minutes and there is no breaking them up. Yesterday this occurred after one of them attacked the nest and ate some fry of my first time breeding tapajos 
- so I was routing for my other loach to kick the attackers butt a little 
I also had just put in a fresh yellow squash in the tank to distract the tankmates for attacking the fry. Below are 2 pics, the 2nd one is of the 2 'grayed out' and on the right side you can see the head of another loach just coining into frame that was not 'grayed out' for comparison. The 1st pic is a 'grayed out' CL and another CL in normal coloriation. After their fight they both returned to normal coloration. 
in case yhou are wondering the brown plastic thing on the bottom of the tank is rain gutter grate from Home Depot and I put that on the bottom as I was aquacaping for protection. My breeding geos would dig it out and expose it within 24 hours after recovering. Also I know wrong spot for it but I'll be selling 2 rockteil sevs for sure and maybe a larger red spot and turquise severum.
- so I was routing for my other loach to kick the attackers butt a little I also had just put in a fresh yellow squash in the tank to distract the tankmates for attacking the fry. Below are 2 pics, the 2nd one is of the 2 'grayed out' and on the right side you can see the head of another loach just coining into frame that was not 'grayed out' for comparison. The 1st pic is a 'grayed out' CL and another CL in normal coloriation. After their fight they both returned to normal coloration. in case yhou are wondering the brown plastic thing on the bottom of the tank is rain gutter grate from Home Depot and I put that on the bottom as I was aquacaping for protection. My breeding geos would dig it out and expose it within 24 hours after recovering. Also I know wrong spot for it but I'll be selling 2 rockteil sevs for sure and maybe a larger red spot and turquise severum.
