Reading over some of the earlier posts, I wanted to emphasize a couple of points that have helped me so far (remember also, I have not been keeping seahorses for that long in comparison to others here although I have prior experience with small reef tanks). But I think I can offer some suggestions for newbies even newbier than me in regards to LPS, SPS and seahorses, I'll use the questions set by timinnl.
1: Can I keep SPS in an all in one tank?
I doubt it...you need a big sump to handle the crap and uneaten food. Have you seen a seahorse's feces?? It's pretty much a big clump of undigested food...like an owl pellet. I use my sump for my filter sock, skimmer (GET A REALLY GOOD ONE), live rocks, bags of Chemipure and Rowaphos, and chaeto along with an insump refugium. On that note, you also NEED a very good clean-up crew. I have 3 peppermint shrimp, a bunch of nassarius, large cerith, and a bunch of limpets and stroma snails that have reproduced in my tank. I'll count my mandarin too since he does eat frozen mysis but only if it's freshly fallen to the bottom.
2: Are the all in one tanks a good design for seahorses or do I need to mod them? (Read this.)
They need to be modded to flow into a big sump and you NEED a chiller. I don't use another powerhead because 1) I think my seahorses could easily get caught 2) I use an over-rated pump to create my flow (700gph for a 30 gal display tank). I keep my SPS near the return outlet.
4: Where should I buy them from?
I got mine from seahorsesource. I love that they genuinely care...the lady I spoke with when my seahorses weren't eating initially gave me a lot of suggestions and really wanted to help.
5: What is the difference between TR/PR/CB seahorses?
Don't even think about anything but CB from a few trusted sites. Captive bred seahorses should NOT be very cheap since they come from seahorses that the owner spawned in a captive system and then raised the fry in a closed captive system and then weened onto frozen foods.
6: Why is the sky blue?
Rayleigh scattering.
7: Can I mix species together?
I wouldn't?
8: Can I mix pipefish & seahorses together?
That's like asking can I mix vampires and werewolves (NO I'm NOT a Twilight fan......). But I'm about to make a horrible analogy: you have to pick a side because either one of those will survive or none of them will survive just from their needs. For that matter, after reading over all the other guides and stuff, don't keep any other fish with seahorses (I keep an ORA blue mandarin but that's only because he eats frozen mysis after I had to re-train him. I wouldn't recommend even him though.)
Oh yah, also, maxing out your credit cards and emptying your savings for your tank helps (jk...sorta).
Avoid like heck all the LPS with sweeper tentacles (torches, frogspawn, plate, Elegance, chalices, etc.). Also, I personally thinks this tip is crucial:I set up my tank 6 months BEFORE adding in seahorses (or any fish). I went through 3 cycles: the nitrogen cycle, the diatom cycle, and the cyanobacteria cycle (that took pretty much the whole 6 months). I supplemented my pod population, added in live mysis and I have a thriving microfauna population as a result (which took a hit when I added in the mandarin but is still doing well...you can even see baby mysis swarming around in the back). I got my corals established BEFORE the seahorses and built up the tank to handle heavy feedings by feeding my corals with mysis and filter feeder food daily). My one acro frag died in this condition but when I saw my Montiporas grow, I knew they could handle it. Taking a risk with my green birdsnest though...we'll see how that pans out.