Here’s a very easy, and CHEAP lettuce clip you can make with just a piece of PVC and a hacksaw.

Cut a piece of PVC about 20mm long, I use 20mm PVC because it forms a nice tight clip for holding nori. Cut the piece length ways with the hacksaw (split the pipe). If you want to stick the clip to the side of the tank put a suction cup on it, I find the easiest way is with one of the cups with a knob on the back, drill a hole in the PVC which will make the knob a tight fit. For my tanks which are small and uncluttered i find it just as easy to drop the clip in and let it sink to the bottom, and retrieve it later when its empty.
Here’s picture if the description isn’t clear enough (note the clip on the upper left has a piece of nori fitted in it.

If you want my permission to use my design just send me $5.00 lol

Bob