The info I’ve compiled on sponges so far:
Most sponges that I’ve looked into primarily consume Dissolved Organic Matter (DOM - sometimes called Dissolved Organic Carbon, or DOC, which is actually a component of DOM) and specific kinds of bacteria (which kinds vary at least a little from one sponge to another). Most of them seem to have no preference for where their DOC comes from, but they have a preference for algal-derived Dissolved Organic Nitrogen (i.e. DON produced by algae). Giant Barrel Sponges and some Boring Sponges have had their diets analyzed, and they primarily consume DOM (~80% of their total diet, with the remaining ~20% coming from Particulate Organic Matter (POM - primarily phytoplankton and bacteria, though, as mentioned above, bacteria is taken in much higher quantities than phyto). This ratio of approximately 80/20 seems to be pretty typical(though it can vary from what I've seen by +/-15% or so one way or another) for most sponges from what I can find.
Unfortunately, we don’t have an easy, hobbyist way to measure DOM, DOC, DON, or POM (or POC or PON) that I’m aware of, so we don't really have any way to determine if the sponges are getting enough food consistently to thrive (to say nothing of measuring the amounts of specific bacteria in our tanks), but there you have it.
If you do some reading on sponge keeping here on R2R, you'll probably find pretty quickly that most people recommend low lighting low flow for sponges (exceptions for photosynthetic sponges), but the truth is this also depends on the sponge species. The most common photosynthetic sponges in the hobby are the photosynthetic plating sponges (like you can find/buy on LiveAquaria's site), but there are quite a few other sponges that are photosynthetic too (such as Aplysina cauliformis, for example), and these would benefit from high lighting. Similarly, some species of sponge do best in very high flow areas, including high flow areas with laminar flow (a lot of people talk about random flow on the site, which would be called turbulent flow, as they're trying to get the water moving basically randomly throughout the tank - laminar flow is just a continuous flow that doesn't change, so the water keeps going the same direction nonstop and there's nothing random about it). If you're not sure if the sponge is photosynthetic or not, you can try starting it in one lighting (such as low lighting), see how it does and then compare it to a different lighting (moderate or high) and figure out its needs from that. Same with the flow. Light will probably be the most important part for photosynthetic species and the food/flow the most important for NPS species - some people have found stirring up their sand to be an effective food source for sponges, likely because it puts bacteria and DOM into the water column. It’s probably safest to start low light/flow and move up, rather than starting high and moving lower.
Some sponges do well in some tanks but not in others for no discernible reason, and some some sponges travel well while other sponges don't. Plus, sometimes a sponge will basically disintegrate into a ton of tiny pieces and look like it's dying, but it'll then proceed to grow and live on afterwards. Similarly, some sponges grow invasively while others grow incredibly slowly, so a lot of keeping these guys at this point really just depends on the luck of the draw (so to speak).
