Water temperature is very important in Aquaponics. There are three main living parts that you need to think about in your setup.
They are:
Plants. Fish. Bacteria.
The general rule of thumb is to keep your water temperature between 18-30°C, unless you have tropical fish. In that case, you'll need to keep the water temperature around 26-27°C. Its all about compromise and balance.
Water temperature is not only important for the survival of fish and plants, it is really important for breakdown and uptake of nutrients and waste. For example, (in simple terms) ammonia is a "waste" product that fish produce during the cycle and can be very toxic to your fish.
Some studies have proven that ammonia levels in colder temperatures have less deadly affects on fish (ionisation). If the temperature is high and the ammonia levels are high the fish may die (unionized) and toxic affect. Anyway, let's not get to science focused right now and stick to simple solutions and facts.
Plants.
Most veggies like 18-30°C.
Some veggies such as lettuce and cucumber like 8-20°C
Other veggies such as basil like 17-30°C
Leafy greens also like to live around 26°C
More importantly, air temperature is not as important as water temperature into the root zones of our plants.
High water temps may result in the following:
Heat stress that shuts roots down and forces plants to go into survival mode.
Wilting, elongating, slimy roots turning black.
Failing to fruit
Cold water temps may result in the following:
Cold water temps generally cause stunned plants and slow growth.
Fish.
It's important to understand that fish have to live within certain temperatures. Unlike plants, fish can't deal with big changes in water temperature. High temperatures increase the metabolism, respiration and oxygen demand of fish. That means the demand for oxygen is increased under conditions where oxygen supply is lowered. The solubility of many toxic substances is increased as well as intensifies as the temperature rises.
Here are some rules:
Tropical fish need to live and thrive between 22-32°C
Cold Water fish prefer 10-18°C
Bacteria.
Bacteria and it's breakdown can be a bit of science, so I won't go into too much of it, but here are some rules that can help bacteria travel through your aquaponics garden.
Bacteria grows in 17-34°C
Temperatures under 17°C will decrease growth rate.
Temperatures below 0°C and above 49°C will kill bacteria in Aquaponics
Snapshot
ROOT ZONE- 22°C. BACTERIA- 25-30°C. GENERAL 18-30°C