Best substrate for indoor pond for RTC?

[vincentwugwg]

I remember ordering a blue liner about 5 years ago with similar dimensions and the one they sent me was patched and i was put on backorder but decided i couldn't wait another 45 days so i went with black. It was a 10ft x 5ft x 3ft FRT pond. Black/Dark turtles on black liner is a terrible combo.

oops the pond was much larger then I remembered... https://www.monsterfishkeepers.com/...ild-50x18-plus-21x18-connected-office.598291/ post #37 has the blue liner on

 

[Hoosiercatfish]

I have double layer of liner but that was for pacu chewing at creases.
if you have butyl liner you should have no concerns about a red tail testing or spliting it. If you have pvc then I may consider a second liner as they get more brittle in time and are more plastic than rubber after a little time under water or lights.
as for the bottom, I have gravel. Again, more for the giraffes than the red tail but find that sand would move way too easily, don't get me wrong, even a 2ft small red tail moves gravel real easy but sand also wears the impeller shafts on pumps real easy when blown around by such a big fish. I also use the gravel as a bedding to put quite substantial rocks into the pond for some of my other fish as I like you have polystyrene base below the liner.
Sounds like you are where I was with one of my first red tails which I also viewed from above but now built a perspex viewing pane into one end and bolted it into the wood frame, trapping and soliconing the liner. Makes all the difference being able to see the fish from the side too.
Good luck, keep posting your story, with some pics.

Thanks that’s useful info I think I’d be afraid of the sand getting into the pump.