Banana and walter worms are super easy to culture and make a wonderful food when the fry are a few days to a week old (depends on growth rate). If you have both types, start with banana worms as they are half the size of walter worms. They live a long time in the water so they make a great “all day” food for very young fry. This doesn’t mean put a huge number in as they due die eventually and can foul the water. If you feed a bit more than your fry can consume, they can eat for a few hours while you are away from home then you can either feed more worms or use baby brine shrimp as another feeding later in the day (which is what I do). I do not culture microworms as there is some evidence that they cause ventral fin burn in betta fry (a lack of ventral fins). So far there is no evidence that banana or walter worms cause these problems.
How to Culture the worms…
You need a container with a lid (to keep fruit flies out and moisture in). Deli containers from the grocery store work well as do round beanie baby cases or disposable ziploc plastic containers. Take whatever container you decide on and poke small holes in the top. I use a thumbtack. Small enough holes to keep bugs out but it allows some moisture and gas from the yeast to escape. Fill the container with half an inch to an inch of cornmeal. I have been using this brand lately because I find it stays solid for a very long time rather than decomposing/getting soupy. http://www.quakeroats.com/products/more-products-from-quaker/content/specialty-items/cornmeal/yellow-corn-meal.aspx
Add enough water to just moisten the cornmeal. You can look from the bottom to see when it is moist through (the cornmeal is much darker in color when wet). I use an eye dropper or needle-less syringe to add the water drop by drop so that the surface stays as level as possible. Once moist, add the starter culture and spread it so it is as flat is possible but try not to get the cornmeal up the sides as it makes harvesting the worms more messy if you touch any cornmeal.
Once you have spread the starter culture, add some bread machine machine yeast, it comes in a jar and lasts a long time, most grocery stores have it on the baking isle. A pinch will do to begin with…moisten with a few drops of water and add the lid. It does take up to a week for a new culture to get going. If moisture forms on the sides of the container, remove lid, wipe sides carefully with a paper towel, avoiding touching the cornmeal. Replace lid, repeat until no moisture forms as the worms will not crawl up if the sides are wet.
Harvesting the worms, really easy, you just take a q-tip/cotton swab and wipe some off the side of the container. You can then swish in the fry aquarium…feed very small amounts until you fry grow big enough to handle more. I feed wardly liquid fry food for the first 7 days or so along with adding a few banana worms as there are some fry that will not be quite big enough to handle the worms right off. At 7-10 days I usually add baby brine shrimp for one feeding and alternate with the worms. If you want to add vitamins to the banana/walter worms swipe some of the worms into a little clear container, with aquarium water, add a few drops of vitachem, let site a few minutes then suck up some with a syringe or eye dropper, then feed. To keep the worms going, add a small pinch of yeast every 2-3 days. If you do not need all the worms, harvest some anyway and toss them out…if you do not, productivity will slow. Eventually productivity will slow down, you will notice that the worms don’t seem to automatically morph into a super population after feeding and crawl in mass up the sides. When this happens, either add a then layer of cornmeal to the existing container, or scoop off the top layer and add a new layer on the bottom and mix the top layer in, in a new container. Some breeders scrape the top level to the side with a spoon, remove what is underneath and add more cornmeal and yeast and mix. I find this messy and I do not like getting cornmeal in my aquarium. Once I can no longer add cornmeal to my container, I start a new culture. DO NOT start all your cultures over at once and always keep at least two going. If you start them over at the same time it may take them a few days to a week to mass reproduce again which can be a problem if your fry are relying on it as a main food source. Once the fry are around 5-6 weeks old I start feeding pellets for one feednig and continue with worms or bbs as often as I can for the other feeding.