For the 20L, the 75 watt moonlight should work (100 if you can find it), check temperatures of course to see where they sit. Your house may be warmer or cooler than mine. For the low-light red bulb, try the 100 watts and see how that does. It may be too warm if you use more heating in your house than we do.
What works as well is just get 100 watts of everything, and then put lamp dimmers on it so you can tweak it as needed.
I haven't tried to use red light heating on a 10 gallon in a long time, so I'm not sure what you'll want to use with that one. Maybe start with a 60 watt (or I think it's 50 watts with the moonlight) and see if that does the trick.
When I tried to heat up a 10 gallon for a baby ball python, I personally couldn't get it to be cool enough on the cool side - It'd be in the high 80's on one side, and mid 80's on the other. After a week of trying to fix it I got mad and got a different tank, lol.
With the ten gallon, if it's for a baby ball (not sure if you're still trying to do the two babies in one tank), you maaay have better luck relying on a heat pad for heat, and just use a really low watt nightlight for viewing.
~jenny
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