Fish rubbing

[LoveTheFishies]

I have noticed a couple fish rubbing against shells and rocks.  It's a newer tank, the fish have been in about 3 weeks.  The pH is 8, nitrites/nitrates and ammonia low, water hard.  I cycled the tank at the beginning and added bacteria.  No signs of ich or other issues.  Eating normally.

The only thing new is a large piece of holey rock I added yesterday.  Rinsed it off before adding. 

Should I treat the tank with salt?

Other suggestions.   Thanks

[Michael Zebrowski]

Do they scratch ("flash") mostly after feeding heavily, or is it consistent?

[LoveTheFishies]

Do they scratch ("flash") mostly after feeding heavily, or is it consistent?

I noticed it after feeding tonight.

[Michael Zebrowski]

Some fish exhibit this behavior after a heavy feeding.  If you're feeding heavy, try feeding less and see if that makes a difference. 

[LoveTheFishies]

Some fish exhibit this behavior after a heavy feeding.  If you're feeding heavy, try feeding less and see if that makes a difference.

Thanks, I didn't think I fed too much, but I'll keep an eye on it.