Nutrient Uptake - Changing Water Every Two Weeks and Testing

by Eric Bacca
(Huntington Beach, CA. USA)

I would like to know about when you suggest using two reservoirs- one for nutrients one for the water. Would this system be a recovery system? and wouldn't I need a third reservoir for the used nutrient and water mixture since the other two are separated?

Do you use a fertilizer injection system? I have been reading that a lot of commercial or large hobbyist do not ever empty the reservoir....only replenish low levels and correct nutrient imbalances. I have a TDS /EC meter which I use. How do you tell what specific nutrients are being most used each day or over a period of time?

Also do you ever have a problem with salmonella, and how do you take your preventative measures to reduce the risk? Have you ever tried ozone water injection to prevent algae growth and sterilize harvested crops? And have you ever used CO2 water injection to lower pH (if needed) and supply CO2 to the water oppose to the air?

Thanks for the helpful and informative site and
for your time for my inquiry. Best Regards, Eric

Answer: Eric- the point of having a "two reservoir" system is simply that you will have a whole reservoir full of de-chlorinated, room temperature water conveniently waiting for you to "swap out" with the old nutrients next time you go to do a nutrient change. In my particular hydroponic system, I re-circulate the nutrient solution through the system. The nutrient reservoir acts as both the nutrient reservoir AND the recovery tank for the system, therefore I only needed two reservoirs in my example.

Unless you are running ten 1000 watt lights or more, it would not be cost effective to use the same techniques as a person trying to manage an enormous garden. Specifically, the cost of a nutrient injection system to manage your nutrient solution and the cost of sophisticated water tests (way more info than what you get from your TDS meter) that detail the levels of every individual nutrient would both be a waste of money for a small gardener.

Instead, the vast majority of all indoor gardeners use a very different strategy to keep the nutrient solution right. Nutrients are mixed at full strength, and the garden is allowed to feed off of those nutrients for about two weeks. If the water level gets low, the reservoir is topped off in between changes with 50% strength nutrient solution.

After two weeks, the chances are pretty good the plants have fed upon certain nutrients more than others- to the point of causing a nutrient imbalance in the solution. Dump the whole reservoir and start over with fresh water and nutrients. For more detailed information on maintaining the nutrient solution properly, check out the how to grow hydro page.

Personally I have never had a problem with Salmonella, have never used ozone injection, and have never used CO2 injection in the water. I believe the best combat against algae is simply designing your system to prevent any of the nutrient solution from coming in contact with any of the light. I have never had the need to "sterilize" any of my crops, but I do sterilize my hydroponic system in between crops with a 5% bleach solution (and tap water). Wiping down your garden area should also help prevent Salmonella. Hope this helps!