I honestly would not go less than 6 as it is hard to balance density with not leaving dead brine. Especially if you're putting them in a 10 gallon. The more the better. I'm not saying it can't be done it requires much more maintenance and monitoring. I would be careful with the intakes as stated. As well as if you have fry (which is a pretty good chance). They are extremely tiny and will find a crack or seam in your tank if you have one. Even if you don't know you have one, they will find it. I also don't know what you've read on them but they NEED enriched
baby brine. I did a study when trying to enhance their color and found out that just newly hatched baby brine is not nutritious enough as the adults were slowly dying in the tank fed un-enriched food. If you're feeding copepods or amphipods you'll have to do your own observation with that. I feed baby brine only. Watch the water current too. If it becomes too strong they simply will starve to death because they are lazy and choose death over moving. When I've observed them eat they often will not let go of whatever they are hanging on to and if the food is too far away they give up. If you wanted to keep smaller amounts of horses too an option is to put a gorgonian in there with them. The gorgonian will feed on whatever you feed.
