Do I need to replace nutrient regularly if I use an aerator?

[audax]

I'm new to hydroponics and I have set up just one beefsteak tomato vine as a test. It is growing exceptionally well, it's about 150 cm high, still growing and is covered in flowers and fruit. I have a 30 litre reservoir with a tiny aquarium pump feeding a constant stream onto the top of the roots (maybe 100 l/hr?). The grow tub over-flows back into the reservoir and holds about eight litres of nutrient, 250mm deep, just below the pot of clay balls. The root growth is substantial and looks healthy - white to gold in colour. I have just today installed an air pump with two small air stones. I have done no pH or EC testing although I have ordered some gear to do this.

As insurance, I have been dumping the nutrient every two weeks or so. Should I also rinse the roots - say with a spray nozzle? Clean the tubs?

My key question is - with the new aerator, do I still need to replace the nutrient? If so, should I do so with the same frequency? Next year, I propose to set up four plants in a system that will hold 100 litres of nutrient. That will cost about AUS$8 every time I drain the system - I'd prefer to avoid that if possible.

[imafan26]

If you are doing Kratky you would not have a pump, only an aerator in a very large reservoir. The nutrient solution would be put in only once and would not require monitoring. However, the size of tank that would be required may not be practical
https://www.ctahr.hawaii.edu/hawaii/dow ... method.pdf

If you are doing a dutch bucket and you are either adding water changing the osmolality in any way,you need to be monitoring with the ec and adding pH up or down or whatever amounts of nutrients are needed. Tomatoes are harder than lettuce because it is a longer crop and nutrient requirements change with the different stages of growth. Replacing the nutrient solution every couple of weeks does get around the some of the problems with balancing the system, but it does get expensive. If you are doing the monitoring as required and adding the corrections, you would not need to drain the tanks completely until after the harvest is complete. You will have to test it daily like a swimming pool and adjust the pH and add nutrients as needed.

https://cals.arizona.edu/hydroponictoma ... tritio.htm

[audax]

Strictly speaking, I don't believe that I'm using either the Kratky or Dutch Bucket method. I'm just constantly recirculating nutrient over the top roots of a plant whose bottom roots dangle in about 250 ml of nutrient and are vigorously aerated - how would you describe that? I think of it as a deep water method.

I forgot to mention in my initial post that my plant (now three months old) is outside in full sun in a coastal Oregon-type climate on a farmlet with a Bass Strait (effectively ocean) water frontage. Water is all rain water. Air temperature in spring-summer-autumn ranges from 10°C to 40°C. One plant is drinking about 3 litres of nutrient per day.

Thank you for the Kratky journal article reference - that will make interesting reading.

My system is based on that of a friend who doesn't drain his nutrient and has never tested pH or EC - he just produces huge (700g and bigger) tomatoes in industrial quantities from two plants - lol. With an engineering background and an inquiring mind, I prefer to know a bit more about what's happening but, then again, why fix it if it ain't broke?

I'll leave the system's nutrient unchanged from now on and I'll monitor its vital signs and adjust as necessary.

[audax]

- how would you describe that? I think of it as a deep water method.

I've decided to call it the Constant Level Oxygenated Recirculating method, otherwise known as the CLOR method.

[applestar]

I thought it sounded kind of like like aeroponics. I’m going to try something similar adapting airlift pump designs so I won’t have to get water pump.

[imafan26]

If your friend puts in the solution only once and does not drain or allow rain water to enter the system, then it is more akin to Kratky. In a Kratky system the solutions should evaporate. during the course of the plants' growth. The air roots will develop in the space and the water roots will stay in the solution.

The other method I know of that is similar to yours is nutrient film technique. Instead of ebb and flow where the solution is allowed to fill the pot intermittently, the nutrient solution is just run past the roots either from the top like the dutch buckets or a in a rail system.
http://www.homehydrosystems.com/hydropo ... stems.html
https://university.upstartfarmers.com/b ... ket-system

In an aeroponic system, there is very little media to support the plant. Nutrient solutions is constantly run over the roots and the water goes back to the main tank. Like a tower or rail system.
In a raft system The bottom of the pot initially sits on top of the water and the roots grow directly in the water of the reservoir. The water is circulated with a pump and aerated to increase oxygen to the roots. Traditional raft systems, the tank needs to be monitored and water and nutrients are added regularly. In a Kratky system, it is static, no pump, just an aerator. The nutrient solution is put in the tank initially and the raft does not float on the water but remains at the same level. The water in the reservoir evaporates the air roots occupy the space and the water roots are in the water. The system usually is for short crops and does not have to be monitored or added to, until the plants are harvested. it is a good way to grow short crops like lettuce which are ready in 5-6 weeks and don't grow so tall that they need a support.
http://www.homehydrosystems.com/hydropo ... stems.html

[audax]

As Kratky explains in his article, the Kratky method is useless for tomatoes.

Maybe I'm not explaining my system (and that of my friend) very well. The nutrient level in the grow tub is constant - it never drops below 250mm deep. About 140mm of roots are above the nutrient, the rest (which are substantial) are submerged. I constantly add nutrient to the reservoir - currently at the rate of 3.5 litres per day. The tomato plant now has about a dozen large fruit that I estimate to be about 400-700g each. They have not yet begun to ripen. Air temperatures are still high - today was over 30°C.

Some further reading suggests that the nearest analogy to my system is the Deep Flow Technique (DFT). Mine differs in two ways: firstly, the roots are oxygenated directly by a large air stone directly below the roots and secondly, the nutrient input to the grow tub is fed to the top of the roots. All of the DFT setups that I have found so far oxygenate the water in the reservoir and feed the nutrient directly into the body of the grow tub. I suggest that an air stone within the root mass ensures the highest possible uptake of oxygen and placing the input at the top of the roots ensures that the exposed roots never dry out.

Back to my first question - do I need to drain the system regularly? And thank you for your patience.