Equipment noise stressing fish

[lmhicks101]

I’ve looked and found a few things on this online but wanted some of your guys opinions. For some background, I have a 29 gallon with a tidal 55 and a nano co-op pump and medium sponge filter.
 

Lately I redid my tank from fluval stratum to hth pool filter sand and love it. However several of my Kuhlis have been stressed out glass surfing. Waters clean, lights the same as it has been, no stresses outside of the tank. No tank mates being dicks. Food is on an auto feeder and I still drop in some treats. It’s been 2 weeks and still flipping out.

I’m grasping at straws here but I never noticed it until now but my filter and pump make some noise. I put my ear to the tank and that tanks a bit noisy. Yes it’s no different then before the change and it probably just comes down to new environment stress but only a few do the surfing. Any ideas on this and anyone have opinions on noise in the tank causing stress? 
 

[gardenman]

I don't think there would be an issue with typical audible noise. If you're keeping elephant noses, dolphins, or other mormyidae species then stray electrical noise/voltages could be an issue.

My suspicion is they're nervous about the color of the substrate. A dark fish against a light substrate makes for easy pickings for a predatory fish/bird/whatever. They may be trying to swim back to the old substrate. (Which would be a challenge for them since it's no longer there.) No human, or animal (including fish) wants to make it easy to be a target for a predator. A dark fish against a lighter colored background is kind of like dropping someone off in polar bear country in a bright orange coat. You'd stand out against the snow and any polar bear within miles could see you easily. You'd be more comfortable (well, as comfortable as anyone could be in polar bear country) in an all-white camouflage outfit.

It's an "everything eats fish" world out there and a light-colored substrate can make a darker colored fish stand out, increasing its chances of being eaten. And by and large, most fish don't want to get eaten. I could be wrong about that, but I suspect in a few days they'll settle down a bit more. They may start hiding out more, but once they accept they can't escape the white substrate, they're apt to go back to being a bit more normal.

[lmhicks101]

@gardenman I didn’t think about that. I thought maybe the light substrate reflecting more light could be an issue but that makes sense. Thank you. 

[Mr. Hollywood]

Maybe run a dimmer light.  Make them feel less exposed.