You could try feeding them these Tetra blocks before you go away on vacation as a test. Cut up a block into quarters or halfs and leave them in the bottom respective areas. Though I have never tried the gel feeder block for my Beta, I have given him the white plaster blocks and he has eaten it. I would prefer not to use the white plaster as it will cloud the water if used long term and in bigger sizes but if it's only one Beta then it should be ok. I will try the gel feeder and see for myself so I know for next time for my Beta but my goldfish love the product. It does not cloud water or leave any messy residue or make the water smell. Both my goldfish Orandas ate the whole block when we went away during Christmas for 5 days. Initially they picked at it and was curious but I am sure they figured out that it's a new form of food and probably devoured it in no time. It's a great alternative to automatic feeders but if you are going away for more than a week then I would suggest an automatic feeder or get someone to help you feed your fish but be careful who you ask to help you. My neighbor killed my other Beta when we went away for 3 weeks by overfeeding it and the water became brown sludge when I came home!
Not sure about the Danios as I have never had them so you can also try with them as a test. I am sure all fish have a great sense of smell and can figure out that it is food. It won't hurt to try so you will know for next time.
My Beta looks for food on the bottom as well as the top and he loves his pellets, frozen blood worms and peas. I feed my goldfish and Beta cooked, peeled peas in combination with pellets as their main staple diet. Peas aids in digestion and gives them an alternative to vegetables in a convenient pellet form. Both Beta and Orandas love peas and gobble them up hungrily like they haven't eaten for years! Good luck and have a great vacation!