I've got a few points to make.
Gel food is great for goldfish, but I think you've gone about it in the wrong manner. It's best to follow recipes that have already been made by experienced and knowledgeable goldfish keepers rather than make your own. Oatmeal should not be used as it is a grain and can cause bloating issues in fancies. Your source of protein should be fresh fish and not pellets as all pellets contain wheat which is also bad for the goldfish GI tract. Gel Food Recipes
This has some gel food recipes that require a blender, but I prefer babyfood gel food recipes. This is the one I use from the GAB:
The GAB Baby Food Gel Food Recipes
Originally Posted by Wendylove @ the GAB
6 jars of baby food, garden vegetables 4 ounce size
can of salmon [small can tuna sized]
cup of boiling water
4 packets gelatin
1 multi vitamin (without iron)
Boil the water, add the gelatin stir till dissolved.
Add the baby food and the salmon.
Dissolve the multi vitamin in a tablespoon of water, add.
Refrigerate till set then cut into cubes.
You can add a half cup or so of finely chopped veggies to this mix as well.
It makes roughly a half-year's worth of food for me; it costs about $15; and is one of the healthiest things I can feed my goldfish.
It's easiest to hand-feed goldfish gel food. That way you can regulate who gets what and how much. It also prevents food from falling on the bottom. I do not recommend getting an algae eater.
Your tank size is entirely too small for a common goldfish. Even with a strong filter (your filter on that tank should be rated for a 55 gal and up), it will not provide enough swimming room for a fully grown common goldfish. Common goldfish should be housed in a 55 gal minimum. A 75 gal or larger is better. And a pond is best. A 29 gal is suitable for two smaller fancy goldfish, but even then I don't recommend this size tank for goldfish. A 40 gal as a min is best.