I have recently been wanting to get a feeding ring for my tank to have open space in the floating plants. The ones that I found available online were not to my liking e.g. the color, size, or the price. I've tried the air line tube DIY and could never get it perfectly round, flat, and air tight. I later noticed that deli container lids and lips had a similar shape as some acrylic rings I saw online, only with some extra plastic attached. That lead me to this simple cheap DIY solution.