The best answer to your first question is an "educated guess" based on research that I have read regarding uptake and internal plant concentrations of specific nutrients. Let them spend their money on lab testing and whatnot. There's actually quite a bit of info out there from university ag extensions. And then from about 6 months or so of my own anecdotal tests adding specific elements to buckets and seeing how long it would take to deplete which in itself can be meaningless since plants will uptake certain elements even when they are not needed which can interfere with future uptake of needed elements but combining everything together with the fact the some elements are stored for future use and taking note of what the plant is telling you, leaf and fruit diagnosis, you can get an idea of what is needed and being used. Plus certain elements are taken up faster than others. If you start with a well balanced 500ppm solution and let it run a plant is not going to uptake it all equally meaning in two weeks or so you won't have 0ppm. The ppm, or EC, of the solution will bottom out at a level where everything the plants can uptake has be taken up leaving the less needed and slow uptake elements. Put that all together with some other stuff I haven't mentioned because it gets confusing very easily and one can make an educated guess which seems, thus far, to proving good. Luckily there is a built in margin for error since plants can handle some imbalances just fine if they occur. This mostly applies to larger fruiting plants that have greater needs. The Kratky method where you never top off or add nutes shows that you can run a res for a month, for something like lettuce, with no additions and have no issues if the solution is well balanced to start. Try that with a fruiting tomato plant and in about a week and a half and your solution will be basically depleted of anything the plant readily needs. It'll survive for a bit on stored elements but then will show signs of deficiencies pretty quickly. I see it on quite a few plants that people show here when they are trying to do too much with Kratky. But I digress. That sounds really expensive for an air pump with that low of an output. If you ever go a different route you can surely find something better online. I use 2-inch air stones in my buckets that are $3. There's definitely an outlay to start a decent hydroponic system and frankly after running costs are tallied you're lucky to break even as compared to just buying it at the store for most plants but it's nice to walk into my room and grab some tomatoes and herbs and go cook and not be needing stuff like that and have to run to the store or have it go bad and be completely wasted sitting in the frig. Plus, it's a relaxing hobby. Anyway, my fingers are tired from typing.

Thanks. Didn't consider dwc, mitchnc, as I wanted to start as simply and inexpensively as possible for a first try. My only investment adding to what I already had on hand was a new $1 BPA-free container, and I finally got to open up a bag of CaN (to supplement the complete, but low-range Ca, fertilizer) which I'd bought for about $5 a while back. Although they were certified tested, when I try again I'm going to use a different batch of seed that I have on-hand - in the remote case that the seed harbored any pathogens - and I'll attempt to encourage better air movement. (Besides checking the water level a bit more often :)

This method seems VERY SIMILAR to the german self watering pots I use. you put your plants in the top and then the water reservoir is in the bottom. they use what is called pon as the soil - similar to gritty mix (no net pot). the roots grow very quickly. they are called lechuza pots and are kind of pricey. they work for not only adenium, but also for african violets. there's a water level thingie that tells you when to water. you also may purchase the pon substrate separately. No. 2 chicken grit and Napa floor dry (part No. 8822) also works. i like the mini deltini this is the taller (not mini) deltini dave

Measuring ph and ec in hydro is important. Good quality meters are more expensive but you only need to buy them once so it can work out cheaper in the long run. It sounds like your TDS/ECmeter isnt accurate because adding nutrient to your tapwater should increase the ppm, not lower it. ;) I dont know what the recoomended dose rate is for Maxigro but for tomato i would use something like 2g per litre and adjust ph to around 5.8 using phosphoric acid (ph down). The EC should be somewhere around 2 including the tapwater. Basil will need a weaker nutrient, i`d start with 1g per litre but wouldnt go above 1.5g per litre. Mix the nutrient in a seperate container, adjust ph and then add it to the system. ,