Aquarium salt primarily works by affecting the delicate balance of water and salt inside single-celled organisms and external parasites through a process called osmosis.
When you add aquarium salt to a freshwater tank, you increase the salinity of the water outside the fish, bacteria, fungus, and parasites. This creates a higher concentration of salt in the surrounding water compared to inside these organisms.
The Power of Osmosis
Here's the key mechanism:
By raising the salinity of the aquarium water, water is sucked out of the bacteria, fungus, or parasite as osmosis seeks to balance the salt concentration on each side of its membrane or skin.
Think of it like this: Water naturally wants to move from an area where there's less salt (like inside a cell or organism) to an area where there's more salt (the salty aquarium water) to try and equalize the concentration.
What Happens to Pathogens?
- Bacteria and Fungi: These single-celled organisms have membranes that are semi-permeable, meaning water can pass through. When exposed to higher salt concentrations, water is drawn out of their cells. This dehydration process damages their internal structures and can kill them or inhibit their growth.
- External Parasites: Many common external parasites found on fish, such as Ich (Ichthyophthirius multifiliis) or Velvet (Oodinium), are also simple organisms sensitive to salinity changes. The increased salt in the water pulls water out of their bodies, disrupting their ability to function and survive.
How Fish Are Affected (and Protected)
Unlike these simpler organisms, freshwater fish have evolved mechanisms to cope with living in water with low salt levels. They actively work to keep salt inside their bodies and expel excess water that naturally enters through their gills.
When aquarium salt is added at appropriate levels, it slightly reduces the amount of effort a freshwater fish has to put in to manage this balance. This can reduce stress on the fish, especially if they are already weakened by illness or parasites. However, significantly high levels of salt can still be harmful to fish, as their osmoregulation systems have limits.
Benefits of Using Aquarium Salt (in Specific Situations)
- Stress Reduction: Helps fish maintain their internal salt balance.
- Disease Treatment: Can help eliminate or control certain external parasites, bacteria, and fungal infections sensitive to salinity.
- Nitrite Poisoning: Can help protect fish from the effects of nitrite spikes by blocking its uptake through the gills.
It's important to note that aquarium salt is different from marine (sea) salt used for saltwater tanks. Aquarium salt is typically pure sodium chloride (NaCl) and should be used cautiously and only when needed in freshwater aquariums, as not all fish or plants tolerate it well.
