Hi, as soon after the stretch when the plants are producing some buds the fan leaves are crumbling. Look at the attached pictures. What is the problem? I am using Lucas formula and Co2? Ph 5.8 to 6.2. 25 degree celcius. Ec 2.0. 65% rH Is it maybe air burn or light burn or maybe some rez problem or maybe are the plants nutrient deficient because they need more nutes when using Co2? Idk what to do… I want to prevent more plants reacting like that. It always starts after the stretching when the plants start to produce buds…
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Odd. Almost looks like too high EC. Are you also regularly (once/weekly) watering the rockwool cubes with reservoir water from the top to keep salts from building up?
How frequently are you flooding? It looks perhaps as if you are going too long between floods, and when the cube is almost totally dry, it creates a super concentrated solution.
Everything else seems in order and it does not look like pests at first glance.
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Could also be Potassium deficiency, as it is in the older leaves and have the tips burnt, but nutrient burn as suggested before is also an option … 
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I think you’re getting nute burn like @vernal says. I would try feeding more often and lowering your EC. An EC of 2.0 is pretty high. It’s not outrageous, but I don’t think you need to be up that high.
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Is maybe Lucas formula not the best choice? Should I switch to the normal general hydroponics (using all the three) regimen?
I have no plain water without fertilizer available, as I need to carry the water to the grow. So I am on a tight water budget.
I wonder if it could be salt build up on the tables from previous grows. Is that an option?
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Possible, but more likely feed frequency needs to be increased and EC lowered to around 1.5.
Lucas works fine. I am not sure the ratio is the problem here, but I’s troubleshoot EC and feed frequency first. I had slightly better results in veg with a non-lucas formula (Dyna Gro) but not what you are experiencing.
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Looks like a possible phosphorus deficiency to me. Check out the 3rd and 4th pics here:
Looks pretty familiar. I know plants using CO2 can need more nutrients, so maybe they’re just sucking up the P at a really fast rate.
Just my two cents!
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when i put the nutes in then i have an ec of 1.8 already. Maybe the dosage isnt right? I use 20 ml of the micro and of the bloom I use 40ml every 10 liters.
Maybe there is something not correct with that?
I water daily.
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yeah it looks like that. hmmm
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Lucas has plenty of phosphorous at 2.0 EC; I doubt you’re running short.
You need to water more than daily, from the looks of it, or use much larger rockwool blocks that won’t dry so much between waterings. The water in a rockwool cube that is nearly dry has a very high EC. Most people in rockwool feed multiple times per day.
Try feeding twice/day at 1.5 EC instead, see if that doesn’t sort things out.
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This was what I thought straight away I have not looked through this thread past this post yet.
Definitely looks like potassium, fits in with switched to flowering and there demands.
Never used co2 before what are temps?
Either there using the nutes up quicker than you’ve anticipated for or you have some sort of lockout , what’s ph? Think iron deficiency can inhibit potassium intake but that’s top of head so check first stoner memory.
I’d flush through thoroughly, at the correct ph.
Adding a mild nutrient solution at whatever ph potassium intake is optimal. That will depend on style of grow charts are easy to obtain via search engines or maybe fac here.
You could remove most of the dead wood but it’s handy to have the odd leaf that’s showing a defitiancy as an indicator of of your taking the right course or not.
You can see viable tissue regain colour again, I find this can be very helpful approach unless this is a trait and is normal behaviour for the individual in question.
Gonna take another look now as old phone meant I had to ditch text to look at photos again 
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Right looking at photos again.
Mistook the lid of storage container for dwc resovoire at first?
Are they just sitting there in grodans?
It’s probably just me I’ve missed something?
But not dwc. Ebb and flo? Unless I can’t see cage?
Never done hydro but phosphorus now seems viable
ebb and flo. I just put them on the lid of the reservoir to take the photo.
how often can i water the cubes per day? I will change the frequency now to two times per day.
can somebody confirm starting point of 1.6 to 1.8 EC (mS) is correct for lucas formula? Because People say 2.0 is already too high? But after putting the nutes in with ro water I start with 1.6 to 1.8 (dont know exactly atm).
Is european formula of ghe nutrients the same as for US version?
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Nutrient concentrations (EC) should slowly fall, not increase.
1.6 should be just fine. I think this problem has to do with flood frequency over EC, though.
You can water as many times a day to keep the rockwool moist at all times. Little cubes like that it is difficult to overwater. 3 times a day is what I’d start with.
Many people using GH nutrients in Europe. The formula may differ slightly but results should be the same.
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Good point. I’ve had plants that I’ve neglected to water look like that a couple days after being watered again.
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Maybe the Lucas Formula has enough Phosphorus on it, but the actual pH range is not the best for the plant to take it …
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Not likely a pH problem.
5.8-6.2 is more or less ideal.
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I agree, but sometimes they say that you should fluctuate in a higher range so all the nutrients intake are available.
If you check that chart you will see that Phosphorus is not much available in that specific range. If it was only nutrient burn all the leaves would be affected, here the new grouth looks fine …
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I don’t grow by charts. I grow by results.
No need to let pH fluctuate. Guys with automatic pH adjusting systems and dosatrons don’t let things fluctuate if they can help it
Point is, I really don’t think this is a phosphorous deficiency caused by completely normal, standard hydroponic pH range using a standard, normal hydroponic nutrient formula used successfully everywhere.
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