The main reasons for flushing a hydroponic system is nutrient imbalance. Hydroponic fertilizers are specifically formulated for specific crops (you can buy nutrients for a type of crop, like greens or flowers), but each farmer grows a different combination of crops in different conditions, and the ratios in which plants take up nutrients is usually just a little bit off.
This nutrient imbalance is also affected by metal components if the system has any. Zinc and aluminum ions can cause toxicities if they accumulate over time. While it’s easy to just use plastic tanks and fittings, or to coat the metal components in your system with an epoxy to reduce leaching, sometimes the presence of metal is unavoidable.
Two solutions: flushing and mass balancing
Most hydroponic growers take care of this nutrient balance problem by flushing the system and starting from scratch with nutrients. This is certainly the easiest method. Be sure to check with your local town or municipality to follow the correct disposal procedure. This practice can have a downside, however, because often the solution dumped from a system when it is being flushed isn’t used elsewhere. This can be wasteful.
The alternative to flushing a hydroponic system is to learn to mass balance. To do this, growers would get their water tested for individual nutrient levels. This usually has to be done through a lab. Then the grower would adjust each individual nutrient to its proper level.
The reason that many growers choose to flush over mass balancing is that lab test can be pricey (you’ll probably have to pay at least $50, and sometimes up to $500). Still, this option can be cost effective, depending on the size of the system and access to lab testing.
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