Strange things in my tank

[Beverly]

I set up a 5 gal tank a few weeks ago. Put a few lbs of LR with macroalgae in it from another cycled tank. The tank is lit with an NO tube. Filtration is one of those sponge filters used in fry tanks powered by an air pump, so there isn't a great amount of circulation, but it isn't stagnant either. I wanted to keep the MA growing so I tossed in some frozen food. Strangely, instead of the food breaking down, a clear gelatinous dome grew around the food. I disturbed the tank while moving the rock around, so the growth has detritus on it. The pinkish stuff beneath the growth is the food. Size of the growth is about 2" long x 1.5" wide x 3/4" high. Any ideas why the food didn't just disintegrate like usual, and what the heck is that growth?



This second strange thing has been seen in my other tanks, most often in my seahorse tank, which has a few flatworms. It's clear and is about a 1/4" in height and has been seen with a brown flatworm in its belly. What do you think it is?



TIA for your insightful answers