Do guppies need aquarium salt

You should not add salt to your fish tank of guppies. You can add salt to a guppy tank, and in some cases (depending on existing water parameters) it is beneficial to do so. (source)
Add 1 tablespoon (Tbsp) of salt per 3 gallons of water. You can pour the salt directly into the aquarium or hospital tank, but some people like to dissolve the salt in a small cup of water first. This level of salt is like using Neosporin topical ointment for a small cut (in other words, it’s not very strong). (source)
As a general rule, salt should not be added to a freshwater aquarium. Salt is an effective medication provided the fish you are treating are salt tolerant. Salt should never be used in aquariums with live plants. Alternative medications should be used with fish that are not salt tolerant. (source)
There are two types of aquarium salt mixes that can fog up the water in a saltwater tank. What is this? The first one is probiotic salts, which contain live bacteria. These, when used in small water changes of under 10%, are okay and won’t cause water clouding. Oct 16, 2019 (source)
This is the process of maintaining the internal balance of salt and water, therefore aquarium salt may also assist with reducing some osmotic stress. For aquarium salt to be most effective, its generally recommended to dose after starting up a new aquarium and every time you complete a water change. (source)
Although plain aquarium/tonic salt (sodium chloride) is sometimes suggested as a good way to increase hardness and improve buffering, it in fact provides very little of either. Marine salt mix, on the other hand, will raise the pH and carbonate hardness quite significantly. (source)
Rock salt and kosher salts are common alternatives to aquarium salt. Both of these are made from pure sodium chloride and don’t have any extra chemical compounds added to them. (source)
However, there’s a big difference between table salt and aquarium salt. Table salt is often treated with chemicals, such as iodine, and anti-caking agents, some of which contain low toxin levels, including cyanide. Table salt is potentially very harmful to your fish, so never substitute table salt for aquarium salt. Aug 21, 2021 (source)