I’ve had mites or something in my Grindal worms before and I set the culture outside in the sun for an hour and that fixed that . Also , stir your cultures really good once a week . I think it’s best to keep them aerated and avoid anaerobic dead spots which give a sour rotten smell . Ed Warner , in his book “Success With Killifish” , says he feeds white worms by nabbing them out with a pair of tweezers . I tried it the other day and it works . They mass around the food and it’s easy but as soon as you open that container and let the light in they dive so work fast .