Red Banded Hi-Fin
Diagonal Bar Prawn Goby
Those should all stay at or under 3" and shouldn't be too bad in a 5. If you got to live aquaria I'd just look at the gobies and see which ones are prawn gobies and which ones will stay under 3". I just noticed the Tangora Goby the other day, he's an interesting looking little goby.
Yes, any of those gobies plus a pistol shrimp. There's generally two kinds of pistols, tiger pistols and randalls. I'd get a randall if you could as they're supposed to be more peaceful, but I have the tiger and its fine. Just different colorations.
Yay! First time salty. FYI, it would be about the same price to just get a 20 long equipment-wise, and you'd have far more stocking options and far more stability. You'll have to top off twice a day.
Yes, for sure. No protien skimmer needed.
Yes that will work. I would use some Matrix in the bottom, and mod the top into a chaetorefugium. Look up DIY chaeto HOB refugium. Basically you put a screen over the output, and get a grow light, and put chaeto in. Chaeto is a macro algae that will grow quickly, eating up nitrates and other nutrients, reducing the need for constant water changes.
You will also need a small powerhead, live sand, and live or dry rock.
Buying Saltwater and RO/DI water will be just fine for a small tank.
Yes you need a lid. A DIY screen lid works great. You'll also need a light. Lorekeeper has a 5 gallon nano reef, he can help you with lighting/flow requirements.
A 20 long (or a 10!) Would be much easier to keep and stock, and I'd recommend it unless you're simply low on space like I am. That said, it's not all that hard to keep a 5.
No protein skimmer needed. They do make small ones, but you'll need to do enough water changes to make up for a skimmer anyway.
+1 for the HOB fuge.
I'm not sure if the goby and pistol pair burrow or not, but if they don't, I'd go without any sand. It'll make clean up easier. If the need sand, go with the minimum you can.
Instead of a screen lid, go to Lowe's and have a piece of scrap glass cut as a lid. It'll cut down on evaporation a lot.
For lighting, I'd go with a PAR 38, made by ABI with a clip on lamp. That's the most economical option. Try to hang it pretty high above your tank, to get the best spread and to avoid frying your corals.
For flow, I'd rely on your HOB and an additional small powerhead or internal filter without media. The Top Fin 10 gallon internal filters make good powerheads in this size tank if you're short on cash!
5 Gallons is very small for saltwater. You really need at least a 20 gallon and the bigger the better for saltwater.. I once had a 30 with just 4 fish in it. A small Blue Angel, a Yellow Tang, a Sailfin Tang, and a Tomato Clown. It lasted 4 years and then broke down and I lost everything.
I looked there and it looks to me that 10 gallons is the absolute minimum if you want to have more than invertebrates. Even then you can only have one or 2 small fish like Gobies. I'll stick with the minimum 20 statement for any kind of decent fish.
Having said that, I see there has been a lot of advancement since I had my tank from 1984 to 1989. Back then, you used an undergravel filter with crushed coral as the substrate. External filters were discouraged, especially if they had activated charcoal in them which was thought to remove too many necessary minerals. They also removed the food that corals and anemones need. It was next to impossible to keep corals, anemones, or live rock alive for more than 6 weeks. The only available food for invertebrates was something made out of crushed peas and spinach and it didn't work well. I had no success with the invertebrates and settled for the 4 fish I mentioned and a Hawaiian lobster. My 30 gallon tank was thought by most to be too small and most people were using at least a 55. With any size, if you were able to keep anything more than 2 years, you were doing well.
Most of the successful 2.5+ gallon tanks on nano-reef have some sort of fish, or multiple ornamental invertebrates. One or small fish isn't bad, and it certainly doesn't make them not "decent". That said, it's always good to have multiple opinions on this forum, and I'm not trying to change yours - just pointing out that many, many aquarists have had major success with keeping fish in pico tanks for the past decade or so. El Fab's 3 Gallon Reef is an amazing example.
But, again, to be clear to the OP, stock light. I have a small damsel in my tank, and he adds quite a bioload. If I didn't plan to upgrade to a 10-20 gallon within the next year, I wouldn't have got him. The shrimp and goby pair would be an awesome stocking, and would keep your bioload relatively low.
Only thing I would watch for with a spray bar is salt creep, and the fact that it's going to be VERY uniform flow. I'd still add in another source of flow personally, or you're likely to get some bad detritus build-up.
If they burrow, it's fine to get sand. Just don't add TOO much, and keep it cleaned as well as possible. I'd recommend some nassarius snails to help!
You could but you will need to watch the tank like a hawk. Personally I feel that it's best to do a 20 gallon long to start as it gives you far more stability and flexibility with stocking options and the cost isn't that much more than a 5 -10 gallon tank since you will need similar equipment regardless: