I'm running a humonia system. My flood and drain beds are not doing well, but my raft area is.
As you can see from the photo (taken mid pump cycle), the only portion of the F/D area that is ok is the area directly around the inlet pipe ... which drips most of the day.
I asked this same question over on the main forum, and was told that my flood and drain cycle (at 4x per day then, and none overnight) needed increasing ... some said every 30 minutes, some at least once per hour.
I have increased it to the maximum I can on this timer and drain system, it is now at 20 cycles per day, and there is some improvement in the plants, but not much.
Some of them are a bit greener, but that is all.
So from a purely 'fishless' perspective, what do you suggest?
I've seen several references on this group to flooding only twice a day, and that in a fishless system you don't need to do it so often.
So ... how often should I really be flooding my system?
And is that likely to be the main problem?
If I can't get the flood area working I will rebuild and make it all raft, but I don't ultimately want to have to do that ... and I just don't see why it should not be working when everyone else's flood and drain beds work just fine.
(I know I have a black thumb sometimes but really this is ridiculous)
the one that is doing ok are using the same media ? what size media are you using ?
Are the beds actually flooding when the timer comes on? You might try bell siphons. We need more details including test kit results. We don't have much more than your picture to go by. More pics of it flooded, etc. could help. Have the seedlings been dying or are you starting from seed? and so on. A flow diagram would also help. It really makes no sense. There must be something we are not getting.
You want to flood your system as often as it takes for the media to stay moist and not dry out.
And you don't want to convert to all raft beds, because its in the bio-filters (your media beds) where the humonia is being oxidized into nitrates.
Like Jim says, some more basic info about your system (water quality parameters, flow diagram etc...) might help.
But it would not make much intuitive sense for your DWC plants to be doing great, while the media bed plants are not (unless your flood cycles were too few too far between).
All the same media ... in fact the piece that is doing OK is just one tiny portion of a bed that is otherwise not so good.
Its the piece that is under the inlet and is dripped on all day.
The media is scoria fines, with the silt sieved out first ... mostly around 1/4".
The beds are indeed flooding nicely, the water is coming up to within 1/2" probably less of the surface every time, and it wicks right up to the top ... so the surface is quite damp.
Test results ... PH 7 ... Nitrate 30-50ppm. Anything else I should be checking?
I use rainwater.
The seedlings aren't dying as such, they simply never grow. I just pulled out a whole lot of beetroot that were planted in there a month ago and hadn't progressed past the 2 leaf stage in all that time. I've replaced them with some pea seeds.
They do turn dark purple ... but thats pretty normal for a distressed beetroot.
Have uploaded a diagram below ... hopefully you can make head or tail of it.
The 'holding tank' is in 3 parts ... 2 drums, one half with the pump in it, connected by a pipe at the bottom.
The pump splits into 2, feeds the 2 DWC chambers, which overflow into the first 2 media beds, which then level with the next 2 by way of the connecting pipe at the bottom.
Each of the 4 beds has its own drain underneath, which all join together to empty into the first holding tank.
I have been told my media beds should have been first in line because of solids filtration ... but I'm thinking as this is purely a fishless system thats not such a problem.
In your scenario it's probably not that big a deal to have the DWC before the media beds...though even in a fishless system where ammonia oxidation is taking place, I still like to have the media beds first in line before any other planted sub-system (DWC, NFT, whatever...)
Are you trying to grow appropriate types of plants for your area during this time of year?
Are any of your other plants showing signs of 'purple-ing' (minus the beets) or purple streaking (often along the stalks or the undersides of older leaves). This purple coloration is called anthocyanin and is caused by the build up of sugars due to phosphate deficiency. Stunted plants are also one of the symptoms of phosphate deficiency. (I'm not saying that is root of your problem, just a possibility). You can check the status of phosphate in your system with a phosphate checker, or reagent test kit.
Should you find phosphates are low, you can reclaim and crystallize magnesium-ammonium-phosphate (MAP) crystals from your humonia. It will allow you to add the needed phosphates, without introducing all the excess nitrogen. Here is how...
Planting cool loving seedlings in a place that's pretty warm/hot can also cause some stunting.
Much lava rock sold in the US usually comes from chemical filtration plants, where they do duty as filter material before being sold off to landscaping companies, or big box stores...so you never really know what your going to get there (I doubt that this is your problem though).
You should still be checking your ammonia (NH4/NH3) levels even though you don't have fish, for the sake of your bacteria.(You can skip the nitrite [NO2] testing though)...
No there's no other purpling ... I've seen that before in phosphorous deficiency, in fact while the system was cycling some carrot plants showed it but as soon as it cycled it just came right. I found the recipe for struvite then but before I implemented it the system cycled and the purple carrots turned green again so I figured it was OK now.
Its just the worst beetroot that are purple now, the stuff in the float end, carrots (yeah floating carrots don't say it lol), lettuce, cauli, and tomatoes are all good, as are the handful of beetroot under the drip. Only the beds are affected. So I'm thinking its just a stress thing.
Unless beetroot are high phosphorous users ... do you know? Actually aren't beet leaves one of the highest phosphorous foods? That would imply they could be ...
Yes they're completely suitable for the season ... in fact I've got some of the same batch of seedlings planted in soil and they're doing fine.
Don't think the scoria will be tainted ... I'm in New Zealand, and with plenty of dead volcanos around I've never heard of a problem with the scoria in garden centres ... and in the proccess of sieving out the silt its actually all been washed ... and, I've been using the fines sieved out for starting seeds in with success.
I'll check ammonia ... I haven't since it cycled and I'd confirmed that the next feeds disappeared as they should ...
One more thing I've noticed ... most of the plants in that bed have improved slightly with more cycles, although still struggling ... but the row up either side of the drum haven't changed at all, the plants throught the centre flow are doing better than the edges. I'll grab a photo.
But surely this can't be a tracking problem with flood and drain?? I mean it can't not flood the edges right?
Ok some thoughts ...
If the beetroot are deficient in phosphorous, its still not the cause of the problem, because the ones that are at the drip are not deficient. Its only those out of ideal nutrient access that are in trouble.
So, there is still an issue with areas of the flood and drain beds being unable to access enough nutrient ...
but it appears phosphorous is one nutrient its is unable to get in those areas.
I'm not going to be in town for a while so I can't pick up a phosphorous test for at least a couple of weeks, so I'm thinking of adding a bit of struvite and see what happens ...
What is the desirable level of phosphorous I should see on a test? I'm looking in the catalogue of other products by my nitrogen test brand and it has a phosphorous test up to 5.5ppm ... is that adequate?
No, 5.5ppm PO4 may not really adequate for many plants...but what you can do is use double the amount of water you use in the test...thereby bringing up detectable levels to 11ppm. (if you triple the amount of water you bring up the readable range to 16.5ppm so on and so forth)...
Some of those kits/tests are able to test for orthophosphates in solution and not the amount of actual 'pure' phosphorous...but some may present results as phosphorous as opposed to phosphates.
To convert PO4 to P, divide by 3. To convert P to PO4, multiply by 3.