if you are making your own nutes using individual chemicals, then yes you will want to test the pH initially. However once you have a recipe, you don't have to test. If you want to reuse nutrient solution in a to waste system, then yes you would have to test the pH. If you just drain the waste to say landscape plantings then no you would not test that. Hydro is usually done in an inert medium. However, as the u. of arizona quote above shows, non-inert media like sawdust can be used. I will agree that the line between hydro and conventional starts to be blurred by using non-inert ingredients. But I think that the intent of the nutes being used helps clarify that. If you are using nutes that don't require biological breakdown like nitrates it's closer to the hydro bright line. If you are using nutes like urea that do require breakdown and will work on the medium it's closer to the conventional bright line. there is definitely a continuum. Not every synthetic would be hydro. Urea and ammonium are going to require biological activity (yes you can use those in a recirculating hydro setup but the results are generally not great). Those are the most common synthetics used by commercial growers. Nitrate based hydro nutes are much more expensive. A lot of commercial growrrs also use composted bark for moisture retention. That combo is much more conventional than hydro. Those media breakdown quickly and they have to repot evey season. that last bit about organc and synthetic is just confused because of the erroneous vernacular use of 'organic'. Organic hydroponics are just nutrient solutions of immediately available nitrates from 'organic' sources. The whole semi thing cracks me up a bit. 20 years ago if you walked intoa hydro store you would find decorative cotainers for houseplants that were passive systems that look exactly like the semi containers. They were rightly called hydroponics. They were usually from Europe and they would be filled with hydroton or leca. Then along comes one orchid grower in the US that felt that people were afraid of the word hydroponic does the same thing and brands it semi-hydroponics and puts it on the web and poof, people start calling passive hydroponics, semi-hydroponics. Of course, all the people in Europe that are still doing the same thing are doing passive hydroponics. Books on hydroponic houseplants still refer to that system as hydroponcs. But that guy sure gets a lot of hits because he convinced people that semi-hydroponics is something different than what people have been doing for decades.

greentoe, 1) watering frequency... al has said over and over on this forum that he waters according to his plants' needs, and that this is often around every three days. ray barkalow recommends watering once a week, or at a minimum every 14 days, even if a particular plant still has water in its reservoir. this means watering one half to one quarter as often. if you are seeing information from ray that conflicts with this, please post some links, because this is what i remember from reading his websites and orchid forum posts years ago. 2) dan's watering frequency... the critical thing in semi-hydro is keeping a nutrient water source in the bottom of the grow pot. the media needs to stay damp. however, this level needs to be relatively low in the pot so that there is still plenty of 'airy' media above the water for the plant to grow its roots. this water level should be about a fifth the height of the grow pot. it is NOT ok to add water above this line to try to reduce your watering frequency... but it IS ok to add a wider water tray for the grow pot to sit in. the larger tray can hold a larger volume of water, and so you can reduce your watering frequency. just be sure to only ever have a water level height at the proper place. in my case, i set my plants in saucers that are only a tad bigger than the grow pot. these saucers will hold enough water for about a week and a half or so. but, when i travel, i move the plant, in its grow pot, to partly covered trays that hold a much larger volume of water. 6" pots go into those disposable salad boxes with a hole cut in the top to accommodate the pot. and the large pots 10+" go into 12" by 18" plastic trays i found in the organizer section of a big box store. i loosely cover the top with painter's plastic to cut down on evaporation. then i fill them with water/nutrients to the same 1" for small plants or 2" for large plants as i usually do with the smaller trays. with this set up, my plants can easily go 3 to 4+ weeks before they need watering again. the reason i don't leave my plants like this all the time is that ray, and many other semi-hydro folks, including companies who manufacture the media, believe that most plants are healthier with a water level that rises and falls more frequently... such as every week or two. the idea is that a falling water level will pull oxygen into the root zone. a few of my plants, such as some Homalomena "Emerald Gem"s, could care less, but a few of my variegated Aglaonemas lost some of their good looks during a 1 to 2 year period when i was away from the house a lot, and they remained in the 'vacation' trays most of the time. none of them died or anything... but their leaf color was faded looking. they bounced back when moved back into their normal trays. 3) evaporation... remember that most of what ray has written concerns his method for growing orchids in a humid greenhouse. in a dry, indoor home, surface evaporation will be much greater. however, as mentioned earlier, the media surface will dry and act as a kind of mulch of sorts. i, like petrushka, have begun to add a 1/2" or so layer of gravel to the surface of the hydroton. it sounds like my gravel may be a bit larger than hers, but it will work the same. the kind i use is sold as a decorative polished gravel and the pieces are about the size of the hydroton. now, in my case, i'm not doing this to reduce watering frequency (and it won't change it much, if it all). i'm doing it because i think it looks nicer... and most importantly, to help reduce salt accumulation in the media. salt deposits at sites of evaporation, and reducing evaporation will therefore reduce salt deposition. even with this, i still flush all my pots in the shower, or outdoors, every 3 months at least. 4) watering volume... if you read and follow rays watering instructions, you will burn through a LOT of water. his watering instructions are to fill the grow cups (that have two small holes about an inch up from the bottom) to the top with a running stream of nutrient water, and then let the excess drain out through the holes. his plants are beautiful and he has been doing this for years. so his method works. however, to me, this seems like such a waste of water. also, if you search for forum posts where ray talks about his own indoor houseplants, he doesn't water the same way. he merely waters until he has a little flow out of the overflow holes... and then every month or two, he takes the pots to the sink and gives them a good flush with water to prevent salt accumulation. he said that this seems good enough for most house plants. he believes that they aren't as salt sensitive as some orchids. also, houseplants are growing and respiring at a much lower rate than actively growing plants in a much higher light greenhouse. 5) as for 'water roots' versus 'air roots' and such... the short answer is that as dan and petrushka mentioned above, roots will grow down into the water. what you don't want to do is drown the "air roots" by raising the water level too high. they're not used to this. also, for most of my plants (primarily aglaonemas), their soil roots survived the move to S/H just fine. very, very few roots died during the transition. most of the time i don't even tent the plants (though i did water the media more frequently to keep it a bit damper than normal. thinner leaved plants would likely appreciate a little extra humidity though. 6) how i water... first, i never let my plants go dry. if i see a tray that's empty or very low, i usually water all of the plants so that i can forget all of them until next time to water. i don't walk around every two or three days checking on how 'everyone' is doing. when i water, i dump out any remaining nutrient water in the water tray, and then re-fill to the proper water level with fresh solution. never, ever just "top up" your remaining water to the proper level because salts will accumulate. and, as i said, flush with plain water from time to time as well. oh, and i place a piece of blue tape with the level marked on the outside of the drip tray in case anyone else ever needs to water my plants for me. if someone else is watering, this is the only time i 'top up'. i just tell them to water until the water is up to the line. easy, peasy. even a 5th grader can water my plants now. for feeding and watering my plants, i add 1 tsp of Dyna Grow Foliage Pro 9-3-6 to 1 gallon of water. i just use tap water, which here in portland or, is pretty decent tap water. i don't adjust pH or anything. our water is very soft, and a bit on the acidic side. folks who live in areas with hard water will likely accumulate minerals on their ceramic media faster. you might want to try to water with rain water or distilled water instead. you also might be fine as long as you're even more careful about flushing. well, and a gravel top dress might help as well. do NOT use softened water on your s/h plants. i hope some of this helps. i really like this method of growing houseplants. it takes the guess work out of watering... cheers, nancy

Denise, check out this video: http://www.youtube.com/watch?v=pUPsIpd9TmQ. It's salesy, but there is an interesting water absorption demo at 1:10 with growstones vs hydroton. It does not behave as glass, I agree. By the way, the demo has a flaw and causes at least one question. I wonder if they washed that hydroton before it gave off that red dust. I bet they didn't. And even if they did, for our semi-hydro application, you'll just wash the dirty effluent off, no big deal, it does not get pumped back into the more closed-end fully-hydroponic system forever. And the flaw is: note how he places the Growstone largest flat face down. The soaking surface is way bigger - of course it's gonna soak up more water! It's water retention capacity per volume unit in the mix that matters. Now, maybe Growstone absorbs more water by that measure as well, but that is not what is being demonstrated. And another thing I can think of: what if hydroton just needs more time to soak the water up? The plant is not in a rush! Need to measure after some time has passed. >> it is, however, expensive!!! I just bought 1.25 cu ft of the larger Growstones for $22, and Doug says smaller particles are cheaper. Checking large grade perlite (Espoma), it is $15 or so per cu ft., so perhaps the difference is not that large. Delivery fees may change this comparison significantly, of course. If you can buy one locally but not the other, it changes things. As a side note, to rationalize the Growstone purchase and to lower delivery fee, I also bought another 4-bulb 4-foot fluorescent grow light. So, let's see, start with wanting to do a dinky little experiment on semi-hydro, end up paying $137. Yeah, sounds about right. :-/ This post was edited by greentoe357 on Wed, Feb 19, 14 at 13:06

odyssey3 - I don't understand what you mean, the Lechuza Pon is 100% inorganic. I only use the pon, I don't add soil. If I would add soil the biggest advantage of a soilless mix would go away: Air in-between the particles and lack of decomposition. I have one plant (ficus pumila or something like that) in a Lechuza pot with 5-1-1 and it's doing fine. 2 african violets, one orchid, one maidenhair fern and one maranta are potted in 100% Lechuza Pon. I have removed all the old soil. One violet is perky and healthy, the other one is droopy, the maranta is doing great, the fern as well. The orchid (Nelly Isler) has only been in lechuza pon for a day so who knows. I got it for 2€ on clearance.