Richard bray

Temperature
Temperature has an effect on nitrifying bacteria, although the margin for error is much wider than other factors. Nitrifying bacteria operate best between 85° and 95°, although they are plenty active down to 59° where there's a steep decline in efficiency.
This is good news for aquaponics growers, because most systems will operate between 60° and 80°. Plants that need more nitrogen are generally warm-season plants, which also happen to be closer to the sweet spot of nitrification. Leafy greens need more nitrogen than other nutrients, but are much less demanding overall, and can tolerate lower nitrification rates and lower temperatures.
Testing
The only way to gauge the health of your system (before a system failure) is with consistent water tests. Any freshwater test that shows nitrate, nitrite, and ammonia will help you determine how well your system is converting ammonia into nitrogen.
In general, you should aim for the following numbers:

• Total Ammonia Nitrogen:
• Nitrite:
• Nitrate: 5-150ppm
• Dissolved Oxygen: 5ppm

Ammonia and nitrite are extremely toxic for fish, so it’s important to take corrective action quickly if you notice a rise in either value. Nitrates are harmless up to 160ppm, but large numbers at the end of
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your system (before reentry into the fish tank) suggests your system can feed more plants or heavier nitrogen users.
Extremely low values suggest the opposite; your system is maxed out and may be suffering from nitrogen deficiency.
Nitrogen Deficiency
regular testing should alert you to nitrogen deficiencies before your plants, but it’s important to recognize the signs.
The most obvious sign of nitrogen deficiency is yellow leaves. Nitrogen is responsible for green, fleshy growth, so yellow, stunted plants are a classic symptom of nitrogen deficiency. However, it can also be a sign of other problems, like lack of appropriate lighting, or other nutrient deficiencies and toxicities.
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The best way to diagnose nitrogen deficiencies is by testing the water. I If the nitrates are relatively high (above 40ppm), check the other I nutrients and the quality of light.