Mary, it could be very important that you have very little sand in your tank. It has been extremely well documented in the literature on prawn cultivation in commercial systems that Vibrio and other bacteria produce substances that are deleterious to larval development. They also note that ponds get old and have to be replaced, presumably because of limitations in material in the substrate.
As we know, there are a tremendous variety of creatures that live in substrates. They all grow exponentially. If they did not consume each other or otherwise limit each other's growth, the surface of the earth would soon be covered in bacteria. Bacterial growth, as far as I understand it, is limited by bacterial warfare to a great extent- overgrowth, secretion of digestive attacks, growth inhibitors, cell signalling- all kinds of chemical gunk gets put out. Most of this is presumably short range, and is metabolized quickly. However, in our small aquariums, temperature changes, salinity changes, a piece of food on the floor of the aquarium, a minor disturbance with fish digging, advective currents that change randomly- all create a riot of reshuffling of the bacterial populations.
As substrates age, they can put out nitrogen as a gas, but they can't put out phosphate and refractory ash products of metabolism. As in commercial prawn farmiing, substrates reach a limit where production starts to fall.
I believe, as we feed our tanks more, we will see these limits earlier. And I suspect what Mary is doing is going to be the answer- bare bottom tanks with algae filtration.
By the way, there is an OUTSTANDING discussion of plankton and sand bed advection in the third volume of Delbeek and Sprung- read it! My take- sand beds are competitive with filter feeders.
I put in some of the chopped food its only a ten gallon tank so it didnt take much to fill the water with particles. I still didnt get any better response. The lights were on (65 watt LOA PC) so maybe this had something to do with it. Not sure if I should try again once the lights are off. Now I need to siphon out what I put in. Do you think it would be alright to leave it in until morning, or should I siphon it out now?
