matthewkingoftheworld;4390388; said:
"Since the Fire eel inhabits Southeast Asian rivers and streams, it will prefer a warm temperature between 24-27° C (75-81° F), a pH of 7 and a dH of 10. It will however tolerate a pH in the 6-7.5 range and a dH between 6 and 20. Adding some salt to the water is a very good idea."
this i a direct quote from
http://www.aquaticcommunity.com/mix/fireeels.php
Just because a website says it doesn't make it true.
Aquarium salt or normal table salt is just sodium chloride. It doesn't contain things to harden the water. The article says "adding some salt is a very good idea" after mentioning dh, without giving logic as to why those two things are related.
Are they suggesting adding some other type of salt (Magnesium chloride, calcium chloride???) which will harden the water? Are they suggesting adding sodium chloride and don't understand water chemistry? Are they suggesting adding sodium chloride for some reason not relating to water chemistry and just happened to mention it after mentioning dh?
And besides that "adding some salt to the water" does not suggest keeping the fish a brackish water setup. Brackish water is attained with salt mix, which raises the alkalinity and hardness and also the salinity. Adding a little bit of aquarium or table salt to the tank does none of that (unless dumping large amounts in you won't have any noticable salinity difference).
Fire eels definitely should not be kept in a brackish water setup. They are built to osmoregulate differently than brackishwater fish. Their body is built to uptake salt and expel fresh water (like all strictly fresh water fish). In a brackish set up their body will be put under a lot of strain trying to expel salt and retain water (which strictly marine/brackish fish are built to do).
Some fish are built to survive in both brackish and/or marine and freshwater. Their body can sufficiently excrete salt and uptake water (when living in high salinity), or excrete water and uptake salt (when living in freshwater). Fire eels are not one of these fish. Their osmoregulatory system is built to work with freshwater environments.
while they may survive for a certain amount of time, they will have health issues down the road or die from being kept in brackish due to osmoregulatory stress.