Your lfs is sticking their nose over your hobby with a wrong advice.
Baking soda has nothing to do with ammonia. Only the bacteria can remove ammonia via conversion to nitrites and plants can possibly consume ammonia.
Baking soda, as far as I have research further, is used to raise the KH(Carbonate Hardness). It cannot neutralize whatever water stats(not even nitrites and nitrates). Not applicable to ammonia but only to hardness level.
I know this info is not much detailed.:mrgreen: But this is all I can help you.
The only things that Baking Soda will do is raise you pH and KH. This is good if your KH is extremely low and willhelp to prevent stress from small pH swings but is useless otherwise.
Stop adding it or tell DH not to unless you need it for tap water that is very acidic. This could be from high levels of CO2 in the tap water in which case you need to let the water sit before adding it with an airstone in it to get it back to levels that won't shock the fish every time you change water.
I used to follow advice from LFS until I found AA and other forums, now I tell them the information they need to know and thankfully they use it. It isn't their fault most of the time that they get no training. Like when I was told that the Red Melon Sword wouldn't get that big and a 10 gallon was plenty big. 3 months later it grew out the top and filled 4/5ths of the tank.
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