I present to you a tale of unfortunate events and sort of a diagnosis Koan. A koan is a paradoxical anecdote or riddle without a solution, used in Zen Buddhism to demonstrate the inadequacy of logical reasoning and provoke enlightenment. This particular tale does actually have a solution so it is not a true Koan but at the time it seemed like there was no solution or logic to the problem, and only by breaking free of old inadequate logical thought processes and developing new inadequate logical thought processes did it become apparent.
My system at the time was a vertical system using guttering for trays, push-fit plumbing pipe, brass 15mm plumbing gate valves to control flow at each outlet, and a couple of central heating pumps feeding everything. The system was running well for a year or two with no problems. I was at the point of fine tuning and making small improvements. Life was good.
The unfortunate events started January last year when I got an RO unit. During the next cycle, I had what looked to be a Magnesium deficiency. Necrotic blotchy older leaves starting a week or two into flower, progressively getting worse.
I checked PH and it was stable between 5.8 and 5.85. OK, I thought, I expected some changes from fitting the RO unit and adjusting CalMag was one of the main ones. This is no surprise.
So I adjusted the doser to put more CalMag in. No change except the leaves which were OK went darker green. The necrosis still advanced. That cycle finished so I tried to address the issues I was having for the next one. It is now early April.
I tried a different brand of CalMag. No difference.
I then looked for a brand of CalMag which had less N in it. They all have N in to varying degrees but I tried Plant Magic, which looked to have the least. No difference.
Each of these tests took at least a month so from the initial problem, we are now at about mid June (just rough dates, I did not keep a calendar).
I investigated PH, what is PH, and what helps plants absorb Mg. Double checking whether the deficiency I am seeing is actually Mg or not. There is plenty of Mg in the solution, and the PH is bang on for Mg absorption. I move to separate bottles of Calcium and Mg so I can have the ratio I want, with no N.
Now it seems like the symptoms subtly change and get worse. Now the necrosis starts at the leaf edge and works inward on older leaves, which is a strong sign of a P deficiency.
In addition to this, I started to get yellowing of very young leaves in early veg when the clones moved from the propagator to the main system which can be a sign of either Iron def or Sulphur def.
I am now very very confused. I talk to the guy who runs my local shop. He knows things. He gives lectures at universities on plant science, and has worked with the malaysian government on large scale horticultural projects. Often he gets the right answer with far less information than you would think necessary.
He asks the standard environment/TDS/PH questions and points out some areas where my environment is not absolutely perfect (but still OK). He suggests that if RH% is too high or low, this can stop uptake of nutrients sometimes even if the nutrients are available in the tank. RH% was quite low for the early part of veg and too high during flower so I spend a month making sure RH% is spot on, I add a humidifier for early veg and fit a dehumidifier for later flower and make sure ventilation is sealed, tight etc. Just in case I start putting 50% tap water in my tank to eliminate some of the changes made by the RO unit. No difference.
So I bypass the RO unit completely to take me back to before the problems started.
The problems continue. This is very confusing. It seemed like the problems started when I fitted the RO unit but removing it did not make them go away.
The yellowing of young leaves in early veg is worse next cycle, but still goes away when they go into flower. This now has me very very confused indeed. During veg they were at 22-26C 60-80RH% so the environment should not be causing that. One of the more confusing things is that yields remained high, in fact, I was getting some of the best GPW figures I have ever had.
It is now getting on to Sept of last year. It is my wife’s birthday so we go to Portugal for 2 weeks. The ladies are in week 5 of flower. They show strong signs of what I am now 100% sure is a P def.
Just before I went on holiday I mention that it looks like a P def to my shop guy who replies “Then you are the first person in the world who did not have enough P in their tank, there must be another cause. It’s not a deficiency, so you have too much of something else and it is blocking absorption of potassium.” I decide to have a proper think about this when I return from holiday. Initially, I considered reducing TDS levels even further and checking ratios, in case I underestimated the effect from removing the crap from my water and I was overfeeding something.
Whilst in the air on the way to Portugal, the pump which doses PH Down crashed dumping all my PH- into the tank which lowered the PH to 1.9 and put the TDS to 1200 (EC 2.5) or so. When I landed, I saw this, had a little panic, and activated the drain pump remotely to reduce TDS, and dumped loads of PH Up into the tank to get things back to sane values. The PH went back to normal in about half an hour, and then the EC reduced to saner levels after an hour. In total, about 3 hours.
I then worried for the next two weeks. Luckily, I can still do some things remotely. The plants seemed to have stopped feeding so I reduced TDS to roughly tap water levels in the hope they may recover, or at least stay alive to finish flowering four weeks later. I did not know if I would return to OK plants, or dry brown dead things.
It turns out their roots were mostly dead but could still take in enough water to stay alive so they had a four-week flush at the end of that cycle. Yield was around 60% of a normal cycle so not a complete loss, and it was a good smoke. I concentrated on just keeping them alive during this time rather than try to figure out anything else.
I take some more clones and start the next cycle.
As soon as they go into the system they go bright yellow and stop growing.
If you wish to try to guess the problem/problems, this is the point to try. The solution is below and you have all the information needed to figure it out.
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I remembered seeing this before when I had a friend make up some lovely copper piping for my system. The copper blocked either Iron or Sulphur and caused the exact same symptoms. Thinking back to the advice I got from my shop guy, I come to the conclusion that the low PH incident corroded the brass and caused copper to leach. I use my google-fu and discover that iron can block absorption of Potassium.
Ah! I now have an idea of what is going on.
The iron cased pumps and brass fittings would have been leaching ever-increasing amounts of copper and iron into the solution, and this only became obvious when the nutrient levels decreased as a result of getting the RO unit. As the corrosion increased, dramatically so after the low PH incident, removing the RO unit would not have solved the issue.
I replaced the brass gate valves with new ones, and also the central heating pumps, noting that all of them were quite corroded on the inside.
The plants showed almost instant signs of recovery. Green veins, new growth!
At this point, a drain pipe became loose leaking the contents of my tank onto the floor and it drained away, air locking the pumps and leaving the roots to dry out just as the plants were recovering. They were in full light for about three hours, very weak, with very little root.
They died.
I take more cuttings.
The cuttings died. Stalks just turned to slime.
It seems that the low PH incident which killed the roots and the recent deficiencies weakening the new plants allowed root rot to set in. This then spread. Completely my fault, I became too fixed on trying to fix the other issue, I forgot to maintain basic hygiene practices.
So I go full ‘nuclear blast from orbit’, take everything apart, bleach everything for 24 hours (except the metal parts as the bleach causes corrosion). My shop guy does me a sweet deal on an Iwaki MD55 pump, no metal in contact with the solution, magnetic drive, very quiet, high flow(70 lpm), 9M head, fucking awesome pump. Easily outperforms two central heating pumps in series. I use the downtime to double check every connection, fitting, and also remove a box section from inside my room, allowing for another plant.
I take more cuttings. This was 2 weeks ago.
They rooted very well and are now sitting in the refurbished, upgraded system. They are showing good signs of growth.
I am looking forward to this cycle. New pump, environment spot on, new upgraded doser with 6 pumps (PH+, PH-, A, B, Silica, CalMag). There are sockets to connect two more pumps, maybe next cycle.
I have fixed literally everything trying to figure out this problem, even problems I did not know I had. They have no excuse to not grow better than I have previously managed.
I am curious to see how they do when they don’t have a lack of potassium.
I will let you know.
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When I changed the valves I banged out a fair amount of limescale, I assumed any copper would have settled into that.