Hello malangon,
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1) Should the roots stay submerged with the water constantly flowing or do I put this on a timer and do a "ebb and flow" type setup? Why one way or the other?
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I'm guessing the reason your not getting a straight answer is it's not a straight right/wrong question. Especially the way you posed the question, because there are a lot of other variables to consider that would make differences. There is no right or wrong here, just preferences. It's not about which way is right and which is wrong, it's more about knowing those variables, and how well you design the system to accommodate the variables and needs of the plant. You could build two identical systems, use identical
nutrients, place identical plants in each, and run one as a flood and drain (ebb & flow), and the other as a recirculating water culture system (the roots stay submerged with the water constantly flowing).
Then after a month of growing will you see identical plant growth? Likely not. While they will probably be close, you'll likely see some difference. However, if you know the differences between both types of hydroponic systems, what makes them different, and understand the needs of the particular plants your growing in the hydroponic systems. Now you can make adjustments to either system to better accommodate the plants needs so you can get close to identical plant growth in both systems. So you see why it's not a cut and dry this is better than that question?
Now if you gave me all the specifics about the type of plants you plan to grow, how many of them you want to grow, the space you have to grow them in etc.. Then I could give you more of a straight forward answer as to what I would do, and why I would do it that way verses another way. It's always going to come down to preferences, but if I know specifics, I can give specific reasons for my preferences.
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2) I have seen systems with an air pump and air stone. I get it that O2 is important, but is it important enough to to to incorporate an air pump or is that an optional item?
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Oxygen is very important to the plants, some plants more than others. As an example: plants that need well draining soil, and/or don't like wet feet cant tolerate saturated roots (suffocating roots). So good aeration is more important to those type of plants compared to plants that don't mind wet feet. All plants need moisture in the root zone. But the term "wet feet" is referring to water saturation in the root zone. Plants that need well draining soil, can't tolerate wet feet (water saturation) as well as plants that don't mind wet feet. If the plants don't get enough oxygen to the roots, they suffocate. Symptoms can range from slow growth, to wilting, to root rot, to death.
As for the question about is it important enough to incorporate an air pump, or it just being optional. Again, it all comes down to how you design your hydroponic systems, and the plants specific needs. Here the type of
hydroponic system makes a big difference, since what makes the type of hydroponic systems different is in the different ways they supply water, nutrients, and oxygen to the roots. But how well the system supply's these elements is in how you design it. An air pump isn't the only way the plants roots can get air/oxygen.
As an example: in a flood and drain system, the flood and drain cycle makes a big difference in how much air/oxygen the plants roots have access to. The longer the roots are submerged, the less oxygen they can get. Say you have a 30 min on, and 30 min off cycle time. 50% of the time the roots are submerged and the only oxygen the roots can get is dissolved oxygen in the water. But when the system drains, fresh air is sucked in, and the roots then have access to air as well as dissolved oxygen in the water. Changing the cycle time from 30 on/off to 15 on, 30 off, will increase the amount of air the roots can get by 25%.
Even changing the cycle time from 30 on, 30 off (50% submerged), to 15 on and 15 off (50% submerged) will increase oxygen levels in the root zone. I know your asking how. The same way you would suffocate by putting a bag over your head. Even though there is still air in the bag, the oxygen will become depleted, and thus you suffocate. Each time the water cycle's, it sucks down fresh air into the root zone. The longer the air remains there the more depleted the oxygen (as well as co2) becomes. By using shorter, but more frequent cycles, you suck fresh air down into the root zone twice as much. In other words, you would still have a 50% submerged rate, but you would get twice as much fresh air getting to the roots. How quickly it becomes depleted depends on a lot of factors like plant size, root zone space, temp's, etc.. But the point is just changing cycle times in a flood and drain system can change root zone oxygen levels, and just one of the ways to increase oxygen levels by system design.