I strongly advise AGAINST using any cleaning chemicals inside the water heater. Rinsing it all out will be challenging.
All you need to do is flush the tank out. Pull the drain plug, let the water go. After it's empty, get one of these (
click here) attach to a garden hose, insert, and spray the inside of the tank. All those white particles of calcium will spew out the hole. No chemicals!
I have several old cloths washing machine hoses laying around (hot and cold). I took one of them and cut it in half since both ends are the female garden hose end, which fits perfect on a garden hose. This also give me 2 shorter hoses with no end on them.
The washing machine hoses with the end cut off fits perfect in the water heater drain plug hole and works great to flush it out.
Also, that same hose is great for filling your fresh water tank. Push that hose down the fill port and you don't have to stand there and hold the hose at the fill port. It slides down the tube and it also prevents air vacuums from happening when filling the fresh water tank.
Again, no chemicals in the water heater. You'll have a nightmare cleaning the chemicals out.