Welcome to R2R! #WelcometoR2R
Definitely slooooww way down. Nothing good happens in this hobby fast. Likely adding all that stuff too fast caused the ammonia spike and the tank isn't ready to deal with it. Is all you added was the 2 live rocks or did you add other rock such as dry or dead rock...
#WelcometoR2R!!! Waterbox and Cade are other aquariums that are worth considering as well taking a look at a custom tank from Glass Cages (check with @Joe Glass Cages).
#WelcometoR2R!!! Make sure that you enter the Aqua Forest contest and submit as many bonus entries as you can. The details can be found at the following link:
https://www.reef2reef.com/threads/win-a-brand-new-oceanguard-reef-tank-from-aquaforest-and-other-great-prizes-5-winners.1000446/
#WelcometoR2R!!! What are you planning to keep in the tank (e.g., what type of fish, what type of coral, etc.)? Different livestock will have different requirement so a bit more info will be helpful.
#WelcometoR2R!!! Congratulations on the new adventure!
The classic recommendation has been to go with steel, but let's ask someone who has had several tanks that size...
@vetteguy53081 - what are your stand recommendations for a 400 gallon tank?
#WelcometoR2R!!! DIY rock is an option, but there are limitations and risks. Consider the potential for negative impact on the parameters. Additionally, the surface area is often significantly less on DIY rock because of the comparable difference in porosity.
#WelcometoR2R!!! Is the tank fully cycled? Have you added fish or coral? Does anything look especially stressed (everything may looked stressed just because it is new)? You may want to consider verifying your salinity with another meter. Also, you could just do regular water changes with...
#WelcometoR2R! I'm sure others will chime in soon, but if you are building a new house and you know where the tank will be placed then you may want to consider adding a separate electrical circuit for the tank equipment. Good luck with whatever you choose!