Salt is a wonderful tonic for all fresh water fish. Though some handle higher concentrations than others. Salt is used to neutralize the negative effects of Nitrite in your aquaculture system and will prevent deaths, especially during system cycle or increases in temperature. How much salt can I use as a general tonic? Treating fish systems with salt is a very common practice with most aquaculture running at 2000 mg/L. This is quite a small amount of salt in a freshwater system however the nitrifying bacteria and the fish will benefit from this addition as it helps to keep nasty bacterial infections to a minimum. In a freshwater aquaculture system the common salt used is pool salt as it contains no anti clogging agents which can be harmful to fish and it is inexpensive. In aquaponic systems, you are limited to lower than 2000 mg/L if you are growing salt intolerant plants. This article points out the various limits to the use of chloride with plants which is very high. However the sodium accumulation can be an issue for plants and they will show signs of stress at various concentrations. Generally salinity is measured by an EC meter. However, this is a measure of all salts and assuming your sodium chloride is not the dominant species, then this method is not ideal for measuring which makes it quite difficult to determine without laboratory testing. A basic salinity refractometer will do the job but again works on specific gravity and will include all salt compounds in the system. With that in mind, when adding sodium into an aquaponic or integrated aquaculture system, be sure you absolutely must use sodium chloride, or don’t use it at all. The calculator below will provide you with alternate compounds as we discussed here. Talking about salinity with plants, as I said an EC (Electrical Conductivity) / TDS (Total Dissolved Solids) meter will measure all of the metal salts, including your nutrients. If you are already running an EC ideal for the plants you are growing, any addition of salt will push that level above what the plants will handle and you will have reduced yields. This article references the salinity tolerance of many cultivars and is a handy reference for growers. Note the EC measurements. If you are running your aquaponic system at an EC of 1.1 and growing eggplants, even a small treatment of sodium chloride will push the EC over the top reducing your growth. In short, if you are offered advice to put sodium chloride in your aquaponic system, ignore it. How much salt do I need to prevent losing our fish to nitrite poisoning? When cycling a new system we practice putting in enough salt to counter at least 10 mg/L of Nitrite when we start the system. This allows for the Nitrite reading to come up during the first stages of starting a system without any harm to the fish. It is very effective and even your bacteria will love it. When you take water quality readings in your system and nitrite is present, quite often it is present at concentrations lower than you can test for, a question we always get asked is “how much salt do I need to prevent losing our fish to nitrite poisoning?” Often you will read, out there in the world, any nitrite reading you should treat with 1 gram of salt per liter of water or 1000 mg of salt.per liter (1 kg salt per 1000 liters) This is good advice and will work well, but it is also just a little bit of overkill for most of the levels you will encounter growing fish, unless you have done something very wrong. If you have messed up that bad, your fish will be long dead before the nitrite reaches 60 mg/L, which 1 gram per liter advice will counter. One sixth of that (165 grams per 1000 liters) is a good starting point and will protect your fish up to a nitrite reading of 10 mg/L (you know when your colorimetric test kit turns really purple…). Give yourself a little buffer room with the salt but don’t overdo it especially in an aquaponic system where you are growing plants. Sure the plants will consume the Chloride content in the salt, however it is the Sodium that will cause you issues with your plant and it will accumulate over time. Keep in mind some fish feeds will contain sodium to a small level and it will stay in the system unless you exchange water out. To give you an idea a recirculating aquaculture system will generally run at an EC of 1.2 with water exchange and no salt added. The trick to effectively treating your aquaculture system to avoid nitrite issues and not overdose on salt is related to the Chloride (Chlorine) content in salt. Which Salt to Use? Pool salt is the easy answer to that. It is about 8 bucks a 25kg bag so it is cheap and has no iodine or anti-caking agents like table salt. Do not use table salt. There are other metal salts that can be used, which I have written about here. Later I will publish a calculator to cover them all. How Much Salt to Use? At a molecular level Sodium Chloride is made up of 39.3371 % Sodium and 60.6629 % Chlorine and it is the Chlorine we are interested in. Most scientific data on line, like this one here, will advise you will need Chloride concentrations 7 to 10 times the Nitrite level in your system. That makes our life easy. Working out how much salt you need is a simple case of multiplying the nitrite concentration (let’s say 10mg/L) by 10 dividing that by 0.606629. Remember we want 10 times the Chloride to Nitrite so multiply the answer by 10, giving you 165 grams of salt per 1000 liters in the system needed to prevent any issues with Nitrite. Simple isn’t it? How do I apply the salt to my fish system It is quite common for us to simply put it straight in the fish tank. It is better if you have a sump to put it into. However be mindful of your pumps capacity to handle the salt. Often it is advised to dissolve it in a bucket of water taken from your fish tank, then tip that in. Either way works just fine. Free Salt Treatment Calculator If you don’t like to waste time remembering how to calculate how much salt you need, then as usual, here is a free salt treatment calculator for you to use. Keep in mind a basic rule of thumb of 200 grams of salt per 1000 liters of water in one dose will do the job nicely and avoid using sodium chloride in your aquaponic system. How to use the calculator The check box will change the input and results between imperial and metric measurement to help those that still have not taken up the metric system (lol). The difficult part of the imperial system when working with concentrations is, internationally we use the metric system eg mg/L… The nitrite reading is an input box which you put in the nitrite reading from your test kit. Most test kits will measure in nitrite nitrogen and will not need converting. Remember even after chloride treatment the nitrite will still be present and will show up on your tests but the fish will be safe. System volume must include all the water in the system. Be sure to include an estimate of your pipe work and filters. You can select from five different compounds in the drop-down box as described below and the amount of treatment is to the right of that in bold. Sodium Chloride (pool salt) as previously explain should only be used exclusively with aquaculture systems that are not delivering water to a hydroponic subsystem. Regardless of the integration method, sodium chloride should not be used. Potassium Chloride is my preferred salt to use in integration plant and fish systems. Most fish feed contains no potassium and aquaponic system are deficient in this nutrient. Be careful if you are already using a potassium compound for buffering the pH such as potassium hydroxide. Calcium Chloride should be used with caution. It is very exothermic, meaning it get very hot when any amount of moisture interacts with it. Basically it is caustic and will burn you, even the sweat on your hands will start the reaction so wear gloves and add it away from the fish and plants preferably the sump in small doses where it will mix well. Again if you are using a calcium compound such as calcium hydroxide for buffering pH be mindful of the amount you are adding, if too much it will precipitate other nutrient our of water. Magnesium Chloride is handy for any magnesium deficiency and it will generally play well with other compounds. Most aquaponic systems will suffer deficiencies so this is a good one to start with if you are using both potassium and calcium compounds for buffering your pH. Hydrogen Chloride (hydrochloric acid), again is quite dangerous to use especially in a small space. You can use small amounts to treat for nitrite as it dissassociates 100% almost instantly and is about 97% Chloride. However it should only be used where you want to decrease your pH. Be very cautious with lowering the ph too much or too quickly. Often when cycling a system hydrochloric acid can be used to set up a lower pH (good for reducing ammonia toxicity) and will add well enough Chloride to prevent nitrite issues during startup of a system. Purity is an input concentration percentage of the compound you are using. For example some hydrochloric acid is only 30%, some potassium chloride is 74%. So check with the supplier or the label and enter the purity percentage in this input box. The two final results are calculated concentrations of the Chloride and the Element you choose to give you an idea of how much nutrient you are applying to an aquaponic system. The chloride result will always be 10 times your nitrite reading. For example if you input a nitrite reading of 4 mg/L the concentration result for chloride will be 40 mg/L. Please be careful with any additions to any system and be absolutely sure you need to add anythign and use the calculator at your own risk and check calculations….