No
Consider getting a second opinion from a new test kit just so you know for sure that you're not chasing a non-existent problem.
How much waterflow do you have in the system?
What is the PH of the water?
Nitrite at your level are fairly harmless. The only concern is that Nitrite above 0.00 is an indication that something has disturbed your bacteria population.
Any contaminants get into the tank possibly?
Yep, you've seen it before so I'm sure you would recognize it. Keep in mind though that just a tiny amount of it will cloud the water. But, you would at least see a film on the container.
You might want to stop stirring it to let it settle to see if it rises or sinks.
Snake, the salt will always dissolve. That's never an issue. Doesn't sound like this is the case this time but a problem can arise if the Calcium and Carbonate components are not dissolved quickly enough they can concentrate and react into Calcium carbonate. The result is water that has a...
I would recommend picking up a bucket of salt that makes 150 - 200 gallons of saltwater. Saltwater is about 1/2 cup of salt per gallon of freshwater give or take.
Do NOT buy any seahorses until you understand your aquarium and it has been running well for a while.
They're typically good looking, docile, hardy, with a nice personality, and they graze on algae all day. Most Tangs can get stressed living in a 4' tank. Other than the Kole, they need to "open up" once in a while. Tangs can also be skittish.
First off, Hawaiian Feather Dusters have a terrible success rate for the typical hobbyist. Their best chance of success is to leave them alone to find their best location. Typically, they are located in the sand bed facing the current. If yours likes the rocks I wouldn't argue with it.
It's a Feather duster. It's in the Bristleworm Family just like your Hawaiian Featherduster, it's just a different species.
This is not an offspring of your Hawaiian.
Your tank is cycled. If it were me I would continue to ghost feed for a couple weeks to mature the bacteria colonies. Although a fish will probably be fine, the odds of success rise dramatically with a more mature/stable bacteria colony.
I guess I'd say I'm a fan of Rabbitfish, not necessarily Fox Face. The Twin Streak I had was smallish, and FULL of personality. I find Tangs skittish. That said, my next tank will have a Yellow Tang but only because my wife misses the one we had.
Yes, they do better in tanks 6' long or more. But one would have better success in a 4' tank than a yellow Tang would. They do not need the open water swimming like Tangs.