how much nutrients can I mix at a time

[xtsho]

I can mix 15 gallons of nutrients for a blumat setup and they last until they get used which could be two weeks or more. Much of it depends on the nutrients you use. Some are more stable than others. Anything with organic components is going to be much more volatile than straight chemical salts. As for aeration. I don't use an air pump but just a small pond pump running 24/7. It keeps the mixture moving and the movement of the water on the surface provides better aeration than the bubbles from an air stone.

 

[Joe.Grow]

I only airstone tap water for a day. After that I’ll add nutes and ph on the higher range. Next day check ph, if it goes up I’ll bring it down to the lower range for coco. Don’t need to be super accurate here as long as it’s in the available nutrient/ph range.

I tried leaving the airstone in the Rez with nutes and it got really slimy and seemed to not be happy.

Ive drawn up several types of auto watering systems and I’d probably use some type of sprinkler valve and controller as most smart controllers can do seconds now. Power it with a on demand pump and the valves opening for the recirculating and or feeding will auto kick the pump on.

 

[Keesje]

wrong and wrong.
aeration ie a waterfall keeps nutes well mixed. does not affect pH at all in my res. i just got back from 10 days gone and pH was same as when i left. and there is nothing wrong with feeding with a solution that has a higher DO content.

I know that mixing by a waterfall or any other system makes sense. You are right about that.

I did not say that it does always affect your ph, but as you can see on forums for people who have aquariums or keep koi, it can.
Which might be not of interest for most of us, but it is a small possibility.
A lot of professional growers of vegetables on hydro don't also areate their water for that same reason.

There might be nothing wrong with aereating your reservoir to get a higher DO content, but it does not make sense either.
The amount of oxygen in gaseous state around wet roots (For example when the water returned from the tray to the res) is thousands of times higher then the tiny bit of DO in the res when you aereate it.
Another thing, once you strart pumping the water from your res to your tray, the DO will get to the maximum because of the movement of the water.
So extra aereating is useless.

 

[NeWcS]

That's the reason I went to power heads instead of air pumps. The pH would go whacky. Not so with the just water pumps

 

[rkymtnman]

The amount of oxygen in gaseous state around wet roots (For example when the water returned from the tray to the res) is thousands of times higher then the tiny bit of DO in the res when you aereate it.
Another thing, once you strart pumping the water from your res to your tray, the DO will get to the maximum because of the movement of the water.

lots of assumptions here. who said anything about me growing in a ebb/flow tray? i feed my plants drain to waste and the more DO in my res, the more the plants will receive when they get watered.

and most of your arguments have this line in them: "most professional growers...." unless you are a professional grower, your point is moot. if you are, i'd love to see a pic of your greenhouse.

 

[gr865]

If I am not mistaken all that is required is to move the solution in your rez to get enough O2 in the system. Take a spring for example, the water tumbles over rock, pond there is no tumbling, a lake is the same way. They depend on the wind to move the water and they get plenty of O2.
I took the small pump out of my rez and just put a small fan on the edge blowing over the solution. I don't have a DO meter but I believe that fan should be sufficient.
The pH and ppm stay stable longer.

 

[rkymtnman]

If I am not mistaken all that is required is to move the solution in your rez to get enough O2 in the system. Take a spring for example, the water tumbles over rock, pond there is no tumbling, a lake is the same way. They depend on the wind to move the water and they get plenty of O2.
I took the small pump out of my rez and just put a small fan on the edge blowing over the solution. I don't have a DO meter but I believe that fan should be sufficient.
The pH and ppm stay stable longer.

i think my waterfall's main job is to keep the nutes and additives well mixed. when i don't use it, i get more sediment (from my humic mix) on the bottom of my res. the extra DO is icing on the cake

 

[gr865]

I know about the sediment situation, I have been hand watering weekly to apply Great White and SubCulture II. The plug up my filters and once they are stirred in it settles to the bottom. My Canna nutes are clean and I don't believe I get stratification of the nutes.

 

[Keesje]

This is me in a greenhouse where I sometimes help out. No better place to learn then from those pro's.
They use a large reservoir. Still standing water. They add no 02 with airpumps, a venturi, a waterfall, or something like that; the only thing they do is run a normal pump every hour for 5 minutes. This is to mix the res and agitate the water surface. By agitating, the water gets enough 02.
In a smaller reservoir (like homegrowers with DWC) one should agitate the water constantly because the amount of water is way smaller and thus the available DO is consumed faster. And you should 'fill up' your reservoir with fresh DO.

In a greenhouse where they do not use a reservoir, but for example use drain to waste or E&F, they just mix the reservoir and that's it.
The reason they don't add extra O2 is because it makes no sense.
1 liter of air contains about 200 / 250 milligrams of O2, depending on the temperature.
1 liter of water contains about 6 to 11 milligrams of O2, depending on the temperature.
Only wet roots can absorb O2. So when you flood your roots and the water leaves again, the roots are surrounded by a very O2 rich enviroment. Ideal circumstances.
Sure you could add DO to your reservoir, but the amount of DO is extremely small compared to the amount of O2 in the air.

Besides that, there will always be DO in your reservoir, if you use a pump or not.
When using a pump it might be 8 milligrams per liter, without a pump perhaps just 1 or 2 or 3 milligrams. Atmospheric pressure.
But by just mixing your reservoir just a tiny bit, the DO-level will rise fast to it's maximum.

 

[rkymtnman]

well said @Keesje but you would agree that leafy greens like in the above picture require much less Dissolved Oxygen levels compared to flowering plants like tomatoes and cannabis?

 

[Keesje]

There is not that much difference between them. The reason they do not grow heavier plants with this system is because they are more likely to fall over and are heavier to handle. But in principle it could be done. (and it is done)
Larger plants naturally also have a larger root mass. If the reservoir is large enough, it is possible.
The air pressure ensures that oxygen is continuously supplied. When it is consumed by the roots, new oxygen is automatically added.
Even if the roots consume oxygen like crazy, the air pressure ensures sufficient supply. The beauty of physics
Especially if you let the water move a bit. So if the root ball would be bigger, you would perhaps move the water for 5 minutes every half hour instead of 5 minutes per hour.
What is sometimes a bigger problem, with larger root mass, is that 'dead' water stays inside the rootball. So the roots on the outside get DO-rich water, but inside the ball stays only the water where all the DO has been used. This sometimes can lead to a problem with DWC in particular.
With E&F and Run To Waste, you don't have this problem. Once the water is gone, rich air with plenty of O2 can reach all the wet roots.

Some remarks on the E&F/RTW...
I sometimes visit a huge greenhouse where they grow vegetables like tettuce and also even tomatoes.
They use plastic or metal tunnels with holes in the top, similair to the DIY fence posts you see here on RollItup.
But then the tunnels are way longer. Sometimes even 100 meter or more.
They let water in at one end and it flows down all the way. The water goes in at several intervals. So every few meters. This is to prevent that the first few plants use all the nutes and the last ones have nothing left. They give them water a few times per day, depending on the stage of flowering of the plant.
The plants grow in rockwool blocks.
The water comes from a huge res and it is also collected again in a res (these growers can measure their nutes by single components, so they add components instead of an already mixed substance) and is then reused.
These growers also don't add DO in the reservoir. As said, there is plenty of air around the roots one the water has left and dripped away.
One of the problems that can occur though, is if they flood too much, that there is not enough time for the water to drip out of the block. Or that the plant does not absorb enough water and there is still plenty of water in the block. Then the roots don't get enough oxygen. What we call 'overwatering'.
I will have to look for a pic that I took during a visit, but so far couldn't find it.