Because the water is being cycled through the system, there is no need to change the water. Some water may be lost through evaporation. However, if you decide the water level is running low and needs replenishing, proceed with caution. Adding water to the system can throw off the chemical balance of the system, so add small amounts of water frequently to compensate for evaporative loss. Also, because there is chlorine in tap water (used to kill bacteria), you should ideally let the chlorine “gas off” before adding it to your system. This is as simple as filling up a bucket with tap water and letting it sit, without a lid, for 24-48 hours.
One great part about aquaponics is there is very little maintenance required once your system becomes stable. In a stable aquaponics system, the only daily addition required is fish food.
Ideally, you should have a backup power source or battery for situations like this. However, in the event that you do not, a less crowded fish tank means the fish can survive longer without extra oxygen. Be sure someone is checking the system daily.
Ideally, you’d like to have about ppm oxygen in your tank for healthy fish and plants. If your dissolved oxygen is less than that, it may be due to the high temperature of your water (as temperature and dissolved oxygen have an inverse relationship) or an algal bloom. One way to increase your dissolved oxygen is by adding aeration pumps.
The water in your aquaponics system should be between 6.8 – 7.0; however, others have experienced success slightly higher/lower as well. If the pH is too acidic, add calcium/potassium carbonate (in the form of sea shells). Add in small doses. It is much better to make small but often changes rather than a large change at once. If the pH is too basic, add a very small amount of 18% phosphoric acid. The pH will not change immediately, so wait multiple days before adding more and checking the pH. Also, high (basic) pH can lock up necessary nutrients that your plants need to survive. This can cause slow plant growth or cause plant death.
In this case, it is recommended you add pure iron chelate to your water for the plants. It makes iron soluble in water and thus, more accessible for the plant. In addition, it is also used as a way to treat a plant that is producing insufficient chlorophyll.
Your fish need bacteria to break down their ammonia and make it less toxic, but your bacteria need your fish to feed them the ammonia so they survive! We recommend adding the appropriate amount of nitrifying bacteria for your quantity of water, and also adding small tilapia fingerlings (or just a few large tilapia). This will ensure your bacteria are being fed and are growing, but there won’t be more ammonia to convert than they can initially handle. As the tilapia grow and produce more ammonia, the bacterial colonies will be large and established enough to handle it!