Need Advice: How to cover the bottom of your tank

[Coleus]

Well, my tank has no sand or substrate so refugium light gets into my tank at night which bothers some of living creatures in my tank.

What is the best way of cover this? Since it is drilled and bowfrontso it just so hard to complete cover it with black film background, I tried and could not get it to block all the light.

I am thinking of duct tape but then, light still leaks through because the tape does not block out the light.

Any other solutions beside painting it because i really don't want the paint potential leak into my tank water and will kill everything.

Thanks

[cuz]

is the problem light coming in thru the bottom of the tank or the side/back? could you tape up a black garbage bag neatly out of sight?

[Coleus]

through the bottom of the tank

[Megalodon]

I think you should cover your sump and everything with plastic and then paint the bottom black with a brush. If not, consider gluing black acrylic to the bottom.

You could also add a little bit of sand to help lessen the light getting through.

[fkshiu]

It's hard to do if you the tank is already up and running, but many people running bare bottoms use some form of HDPE plastic like Starboard or even cutting boards.

[FitoPharmer]

My tank is BB, but it also has a tile bottom. You can get reef safe tiles that would help block light and promote coraline algae growth. I have seen them up to 1'x6". Then you could tape the seems from below or wait for the coraline to take hold to block the rest. My first tank was BB and the fuge light bugged the main tank for a long time until the coraline covered the entire bottom. My 6' 120G cost ~100$ to do with 4"x4" tile.

[intarsiabox]

There's another type of duct tape that looks like polished stainless steel. It is completely opaque and would also help reflect some of the light back down into your refugium. I'm not sure of the name of it but I've used it in some homemade light reflectors or to improve some cheap store bought ones and it is not effected by the heat and does not come off. It's more expensive than duct tape but still would cost under $10 for the amount you need.

[lastlight]

Great idea. I was going to suggest tinfoil but the tape will be easier to apply. Both will block all light.