I Need Some Advice.

[YouSillyHumans]

Ok so recently I started up a tank and my puffer fish died in two days, wasn't a good experience and was a fairly eye opening one.
 
I have two 10 gallon tanks right now one I plan to house a baby snowflake eel in for a very short time, and one I plan to house the live food in for awhile.
 
I have picked the snowflake eel because it seems cheap, I have heard it doesn't die easy from diseases and I also heard it lives a long time... Sounds like a good deal to me when I see them going for 21 dollars with a 2 week arrive live guarantee. but now I digress...
 
 
Since I plan on housing him and only him in this ten gallon ( With live rock and 1 tiny coral too ) I don't think I need a protein skimmer, I plan however on getting a 50 gallon soon which i'll put him in next ( by himself live rock and some coral again ) and I plan on adding a protein skimmer at this point, good filtration with good water circulation and also some air stones.
 
 
I will get a very tiny air rock for the 10 gallon unless anyone advises against it for the baby snowflake.
 
 
I really wanted an octopus but since my puffer fish died so fast I'm pretty sure the delicate octopuses fate would be the same. I don't really know why my puffer died because all my water levels were fine.. but I chose a very delicate spiny box puffer, was my mistake.
 
At some point when and if the snowflake eel lives to even out grow the 50 gal, I'll upgrade the snowflake then and maybe try an octopus in the 50 gallon.
 
 
 
Anyway those are my plans, but I don't know what to do. I have only just recently started getting into aquariums, I wanted to know am I missing anything for my 10 gallon? Do I need a protein skimmer for a baby eel? Do I need anything else besides live rock, filter, heater, and sand for the 10 gallon? And when I move the baby eel to the 50 I know I would have to invest in a protein skimmer but am I missing anything else?
 
I have 8.4 PH stabilizer because that's what I was using for my puffer, I have water conditioner and lots of instant ocean. I have air tubing and I have not bought an air stone yet... I know this is a lot but I just sort of want to get it all organized in my head with what I need because I feel a little lost and don't want a repeat of my puffer fish. I just need to figure out what I can use that I have and what I still have to buy for both the 10 gal i own and the 50 gal i plan to buy.
 
 
 
 
 

 

[Chad]

If you are just starting out you have picked difficult creatures to begin with, puffers, eels, and octopuses (yes, it's octopuses and not octopi) are challenging to maintain. 
 
One thing you will need if you don't have it is a lid. Eels are escape artists and will frequently die on the floor. Octopus are even more so and their lid must be sealed. 
 
If you use RO.DI water, which you should, and a good salt mix you shouldn't have much issue with pH as long as you do regular water changes. Messing with pH is risky business. It's usually  necessary in reef tanks where corals take up elements in the water that alter chemistry as they do. If it's not a reef tank just do weekly water changes of 10% and all should maintain. 
 
I like protein skimmers, I find they add that last little bit of clean to the water but in a fish only tank you can most certainly do without one. 
 
I don't recommend using an airstone in a marine tank. Really you are best having some good power heads that cause surface agitation. 
 
http/youtu.be/rNlxXRnqp4Y
 
For the most basic FOWLR set up you really just need the basic equipment and rock. If you haven't gotten your rock yet here's an article on how to pick good rock. You will also need a way to check the salinity. I recommend a refractometer as a sure method. 

 

[Corey90]

You said you recently set up a tank.  How long was it up before you added fish?  If you're tank was not properly cycled then there would be the first problem.