Salt is a major staple in every goldfish keeper's supply kit, and it is often used as a first line defense against a host of goldfish problems. Salt can be antimicrobial, promotes healing and slimecoat, and can help relieve osmotic pressure ("breathing"). Trinket, one of our esteemed moderators, wrote on the use of salt here
Because salt occupies such a prominent place in our medicine cabinet, and because the misuse/abuse/prolonged use of salt can lead to a host of problems not unlike the things we are trying to cure, I thought to revisit this topic and expanded a little bit on what Trinket had laid out for us, namely to discuss the use of the specific salts and how to properly measure the amount of salt we need.
1. What type of salt can be used safely?
As Trinket had said in her post, any salt that does not contain additives (including yellow prussiate of soda, anti-caking agents, minerals, or iodine) is ok for use in our aquariums. Most commonly, this translates to using aquarium salt (some manufacturer include API and jungle). Aquarium salt usually comes in larger grains. Additionally, Morton's Canning & Pickling salt has been found to be safe and effective to use. Morton's C&P salt comes in a four pound box (all green or blue/green) and can be found in the salt section of many grocery stores in the United States. Morton's C&P salt is very fine grain (looks more like table salt), and is usually the cheapest option available. The C&P salt is often times 5-10x cheaper than aquarium salt. A box of Morton's Canning & Picking Salt looks like this
2. Dosages of salt & how to add salt to the tank
Depending on the situation, you'll be using 0.1%, 0.2%, or 0.3% salt to treat your fish. However, to prevent osmotic shock to fish and to minimize salt's effect on the tank's cycle bacteria, salt is only added at 0.1% increments every twelve hours to the 0.3% salt maximum. You should never just dump salt grains into the tank. When you do that, your fish will most likely rush to the salt and try to eat it. Salt granules can be very irritating/damaging to fish gills, so you should always dissolve the salt first before adding to the tank. The easiest (and quickest) way to do this is to take some tank water (or de-chlorinated water) and heat on the stove top. Once the water is hot/boiling, you can add the necessary amount of salt to dissolve, let cool to the same temperature as the tank temp, and add to the tank.
3. How to correctly measure out salt for use
Using teaspoons per gallon
0.1% salt is 1 teaspoon of salt per gallon. However, because we never fill our tanks to 100% capacity, always estimate the water volume to be a little bit less than your actual tank size (9 gallons for 10g tank, 18 gallons for 20 gallon tank, and so on). This measurement calls for using level teaspoon, not rounded teaspoon. Also, if you are using Morton's Canning & Pickling Salt, 0.1% salt is actually 3/4 teaspoon per gallon, since the Morton's salt grains are much finer, and so you actually get a lot more salt per teaspoon of Morton's than compared to the larger grained aquarium salt.
Metric system and the scale
0.1% salt is 1g/liter of tank water. There are 3.79 liters in a gallon. So, whatever size your tank is in gallons, multiply that by 3.79, and that is how many grams you need in order to raise the salinity of your tank to 0.1%. Here are some common sizes and the amount of salt you will need to raise the salt by 0.1%
- 10 gallons = 10x3.79 = 37.9 grams of salt to increase salt concentration to 0.1%
- 20 gallons = 20x3.79 = 75.8 grams of salt to increase salt concentration to 0.1%
- 29 gallons = 29x3.79 = 109.9 grams of salt to increase salt concentration to 0.1%
- 55 gallons = 55x3.79 = 208.5 grams of salt to increase salt concentration to 0.1%
- 75 gallons = 75x3.79 = 284 grams of salt to increase salt concentration to 0.1%
If you need to raise salt to more than 0.1%, then you will want to dissolve and add the correct amount of salt to your tank 12 hours later, and so on.
If your tank is already in liters, than the size of your tank is the amount of salt you will need, in grams, to raise the salinity to 0.1% (a 750L tank will need 750 grams of salt to be at 0.1%).
4. The duration of salt use
Depending of the situation, you may be advised (or have elected) to salt your tank(s) anywhere from a few days up to a maximum of four weeks.
5. The consequences of prolonged salt usage
This question has been raised many times - if salt can be so beneficial, why not just keep it in the system for longer than four weeks? There are a couple of important reasons why salt should not be used for long durations. First, like any other treatment, prolonged exposure can lead to tolerance in the case of bacteria and other pathogens, and then salt is no longer effective. Unfortunately, this has already happened because of some very irresponsible breeders/farmers who have kept their fish at low levels of salt. A prime example of this flukes. Flukes used to be very treatable with salt. However, at present salt is no longer very effective against flukes, and we have to resort to other means, such as praziquantel.
Another reason why prolonged use of salt is discouraged is because chronic salt exposure could lead to development of what is called osmotic stress in fish. Fish experiencing osmotic stress may display the following symptoms: clamped fins, disequilibrium (unable to balance itself), excited behavior (darting), lethargic (floating), rapid breathing, faded colors, salt burns as evidenced by blackened areas, and fin fraying.