Salt in your Aquaponics system
The addition of small concentrations of salt to your Aquaponics system is a practice that you may read about as you surf the net gathering information. As with all things, there are advantages and disadvantages.
Advantages
Salt is a wonderful, non “chemical” way to treat diseases and bacterial infections in fish. It is also a good “tonic” in the sense that it helps the mucous coating the fish has over its body. This coating is the fish's main defence against disease attack. Fish gill health is also enhanced by salt by helping ward off or treat attacks by parasites.
The advantage of this procedure is said to be disease prevention. Salt helps to guard fish against fungal diseases such as ‘ich’ and some bacterial problems.
Some operators of home based Aquaponics systems run low concentrations of salt in their Aquaponics systems as a tonic, or disease preventer for the fish.
Disadvantages.
Salt interferes with plant growth/health.
In Aquaponics systems water from the fish tank is used to grow vegetables and other plants. In a recirculating AP system or an open ended AP system any added salt will reach the plants.
Most food plants have very adverse reactions to salt. Some plants such as strawberries will die if there is any salt at all present in the water.
However, added salt in carefully managed low concentrations, can be used and acceptable plant growth, for most food plants, is still achieved.
How much salt to add.
The salt is added at the rate of between 1 and 2 ppt.
Concentrations higher than this can be used depending on the plant types being grown, but as a general overall rule 2ppt is as high as is practical for home based systems growing multiple crop varieties.
There is a need to have an accurate way to measure the salt concentration because the concentration will change as the system is operated normally. Some variables are, water is taken up by the plants, evaporation, water top ups, losses due to plumbing leaks and so on. Any of these or a combination of factors can all change the overall concentration of salt in the system.
A useful way to keep track of the salt concentration in the system is to use a low cost refractometer. Basic but very useful refractometers can be obtained for as low as twenty four dollars, or up to several hundred dollars for the more sophisticated digital instruments. The low cost refractometers are very satisfactory for use in home based systems.
What type of "salt" can be used.
Ideally a pure sea salt should be used. This can be difficult to obtain in quantities that may be needed for Aquaponics purposes. The least expensive readily available salt is Swimming Pool Salt. Make sure you read the label to see if there are any additives, but there usually is not.
Table salt is unsuitable because of the addition of "anti caking" agents and the like rendering it unsuitable to be used for fish.
Other ways to use salt.
Many Aquaponics practitioners prefer NOT to run salt in their AP systems, but rather keep the use of salt as a treatment method if and when a disease problem arises.
It should be pointed out that in a well managed home based Aquaponics system, disease problems for the fish are almost nonexistent.
Diseases such as “ich” ( a gill resident parasite) usually are brought in when new fish are obtained from the hatchery or other source.
Bacterial infections usually only appear when the fish are stressed for one reason or another.
Introduced problems like “ich” are well managed by quarantining any new fish.
This is the time to use salt to great advantage.
Every Aquaponics installation should have a “hospital/quarantine” tank. This tank will not need to be all that large, say, two or three hundred litres (75 gallons approx). Ideally it should have a good quality canister filter attached, but any well constructed filter system like a trickling bio filter can be used. Plenty of dissolved oxygen is delivered to the hospital tank by the return water from the filter and splashing on and disturbing the tank water surface and an additional air bubbler.
Use a higher concentration of salt in the hospital tank. Perhaps even up to 1 or 2 parts per thousand if the fish are to be left in the hospital tank for several days or even weeks.
Short intense treatments can be carried out using concentrations of up to 10 parts per thousand.
Caution needs to be exercised here because not all fresh water fish species will tolerate these high salt concentrations. Check with your local fisheries department for information regarding your particular species.
I have used 10 parts per thousand on Jade Perch, Silver Perch, Sleepy Cod and Barramundi with good success. High concentrations like this are only used for short periods of time, say 2 to 6 hours. The fish are then returned to a much lower concentration for the rest of their stay in the hospital tank.
Another method used with good success is to dunk new fish in a concentraton of 10 parts per thousand for 3 to 5 hours, then place into their regular tank. This is done 3 or 4 times two weeks apart. The fish are kept in a floating basket during this time to make it very easy to treat them. They are just lifted out of the regular tank and into the salt tank . When the 3 to 5 hour treatment is finished, just lift them back to their regular tank.
More on salt in the next newsletter.
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