Make a "fish bowl"
plastic storage bag
(the picture shows a sandwich bag, but I ended up using a quart size freezer bag)
Fill the bag with gel to desired amount. I had about a 1/2 bottle of gel left. Your toddler would probably like squeezing the gel out of the tube.
Add a couple drops of food coloring.
I folded the plastic bag over and taped it to hold it down.
Great sensory fun!