Yellow spots on leaves

You should use distilled water. Not tap. Your first two bottles will work overtime trying to correct the pH of tap water plus all the other additives in tap water that the Grobo is not able to mitigate. I buy my distilled water at the grocery store. Also, you will want to calibrate those probs often under these conditions. You will run through bottles 1 and 2 like a running faucet, so the grow will be more expensive than it’s worth buying new bottles constantly. Swap to distilled water and recalibrate the probs and see if you can salvage the grow. My bottles 1 and 2 barely budged on my first grow. I am using the same bottles now on my second grow. I hope this helps! Good luck! :seedling::eyes::raised_hands:


Hey @Arn,

You got some good advice from @HappyHappyJoyJoy. Use RO or distilled water only unless you want to struggle with issues on and off through grows, definitely worth investing in RO system. I use one called ROBuddie that costs $66 on Amazon and works perfectly, will last a few years if just used for Grobo.

Next, careful with your temps. Grobo claims you can grow in regular room temperature but that is stretching reality a little since water res temps need to stay under 70 degrees to avoid root rot and nutrient block. To help this situation there is a additive you can add to the Grobo’s reservoir called Hydroguard which will allow the plant to absorb nutrients even with dealing with higher temps. If you can’t keep your water under 70 this is a must. I went as far as adding an inexpensive water chiller that keeps my res temps around 65 degrees but this isn’t required.

Also keep an eye on that stem where it meets the cocoa pod. If the stem starts to thin a little be sure to push the cocoa pod up to avoid dampening off. :+1:t2:

There are a lot of knowledgeable people on this site that will help you along. Good luck!


Thanks for both of you reply.
I’ve just orderred a RO system, it should be on it’s way for me next week.
Until then, I decided to make the trip to a garden store and bought 10l of distilled water for the next drain and fill!
The coco pod was still noticeably damp, I used a paper towel to remove a bit of moisture.

I’ll see if I get any improvment on the new leaves in the next few days.


Here’s a quick update on my banana kush :
after draining with the RO water, the leaves that where already starting to develop yellow spot are still getting worse, but the one on top looks very healthy and aren’t showing any sign of discoloration.
Should I get rid of them ? only the 2 first set of leaves got affected, would it be better to let them die off, or should I just cut them ?

I managed to get the temp under 24c, oscilating between a low 22c and high 24c during daytime, but it might be harder to maintain with summer arround the corner.
I can’t seem to find any store that would be selling hydroguard where I live, so I’m guessing a watter chiller is our only option here, plus I should be able to add an air outlet at the back of the room to exaust its output. The space I store the grobo in is fairly small and doesn’t have a proper vent, which could explain why the temps quickly got out of hand.
@Wake do you have any recommandation ? I’ve seen that the CW3000AG is fairly inexpensive and has a fan at the back that I could use, but I’m not sure if it’s correctly sized for a grobo.

No worries on the yellowing leaves, leave them or cut them off, won’t effect things much either way. Once they wilt and start to die, I will normally remove.

When you talk about temp are you referring to water temp or air temp. 22-24 is perfect for air but warm for water. I’m going to assume you’re talking about water temp since you mention the water chiller. I found a chiller online that is less expensive and does the job perfectly.

Easy Water Chiller Setup

The room I keep the Grobo in gets up into the 80’s and this setup keeps my water in the mid 60’s.


Well, since my grobo is in a closed room, the air and water temp were almost the same.
I managed to find a way to let the cool air at night enter the room, and I leave it shut during day time,
Water is at arround 20c now, and air between 19c and 23c, and I think I can manage those value for the next few weeks.
Huge thanks for the linked post, I’m pretty sure I will need something setup like that with the summer heatwave.

The plants looks way happier now with RO, and decent temperatures :partying_face: :green_heart:
The fisrt two set of leaves are now almost gone, but the new one are beatiful, thanks again for everyones feedback !


If you decide to get the water chiller let me know, will help you out. :+1:t2:


It’s now day 29 of the grow, and minus a few hot days, the plants regained a lot of colors.
After having a peak, the root system is cystal clear, definitely better than 10 days ago !

I’m on day 5 out of 14 of late veg, but from looking at other people plants, mine doesn’t looks like it’s growing sidways, and looks a tad smaller, should I think about extending this stage ?

@Wake I’ve ordered a chiller and a smart plug, should be on its way next week, I’ll drop a message here if I have any issue installing it!

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The high temps are stunting its growth most likely. It will hang in there until you get the water chiller set up. I have seen many slow starters end up out growing the Grobo so don’t worry just yet. Water chillers are the way to go in my opinion so good move. I don’t like adding chemicals when there is another option. My water chiller does great, no issues with roots since installing. I initially had the chiller set to 69 degrees but still wasn’t happy with the plants but once I tuned it to 65 degrees, it has been smooth sailing.

We will get you rolling :fist_right:t2::+1:t2:



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  • (#TeamHasGotYouCovered): {:green_thumb:}:

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  • (I Would Let Her Grow Until She Reaches The Bottom Of The Second :two: Fan, -Then- Transition Is Good To Start):


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Thanks for all the link.

Quick update from day 33 now,
I’ve noticed that the plant did suffer from damping off, it wasn’t visible before as I assume this part was bellow the coco pod suface, but looking at the first picture, the fact that it was tilted on the side was probably an indication of that.

The pod wasn’t necesarly damp, just a bit wet to the touch.
As recomanded, I moved it up a bit and secured it with toothpicks, I’ve also installed a fan blowing a it for a few days.
I’ve done a small trim of the leaves that where curling down and obstructing most of the light on the new stems, I’m assuming it was also blocking most of the air flow, maybe the reason why the coco pod never did dried completely.

Appart from the slow grow in the last few weeks, the plant looks really happy now.


Nice job discovering the issue before it’s too late! Fan was a great idea. Be ready with a straw in case you need to wrap that stem.


When should I consider the straw option? I thought of it initially, but if the stem is still a bit wet, wouldn’t the moisture retained by the straw help the rot growth further. for now, it doesn’t looks like it’s shedding anything, happy to try it if it’s a viable option.

Also, my pod never seem to be getting dry, the fan I’ve added helped a bit, but it’s still wet.
Could it be the water level being too high ?

Last question, I avoided topping the plant during that period to avoid too much stress, should I go with LST instead ? I deffinitely got way more node than suggested.
With the plant growing taller than wider, and I don’t want to do a lot of trim on the fan leaves either.
what would be my options from there if the trunk endup recovering ?


If the plant’s stem discolors and starts to narrow. If you wait too long the plant will literally fall over. I have seen plants come back from falling over so you are fine.

It is set to preset levels, just list the lid and look. When looking at the roots look at the underneath of the lid, if wet then it is fine to remove some water but only enough to ensure everything isn’t getting soaked under there. Some get wet, some stay dry, not sure why.

You aren’t too late, top any time after 4 or 5 nodes. For the Grobo I recommend topping. You will end up removing the lower branches anyways because they won’t reach the top of the canopy.

Stay positive, keep an eye on the pod. I used to use paper towels daily to dry out my cocoa pod so your effort can save her. Once you get through this stage, it gets easier.


Learning one step at a time :slight_smile:
I really like playing with stuff, and even though there’s more than I thought, I’m still enjoying the whole process.

I received my RO system this morning and after installing it and testing it for 10mn, the pump just stopped working, everything is setup and I might have to teardown everything to sent it back…
If anyone got any idea on where to start my investigation on how to see what failed in it ?
I also just got the chiller and will be setting it up tomorrow, hopefully I’ll be luckier this time around.

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I have had my grobo for almost a year and am still playing around adjusting things each grow. I like playing around too, I do different techniques on each plant to see if there is any difference in potency or size, so much fun growing.


With some help from the seller; got my RO system up and running yesterday, bottle 1 and 2 didn’t even got used, I’m glad I made the purchase, it will definitelyy be less expensive for future grows !

I also bought wires and magnets to support the plant weight while the trunk is recevering as the straw wasn’t helping much.

So the plant doesn’t look stunted anymore, but she definitely lack the stem development on the side,
more like a lilipop plant rather than a bush, she’s getting there, but still a bit slow for sure.
The recipe will move to transition tomorrow, but I’m tempted to add 7 day to the current stage.
She’s just reached the middle of the first fan, should I do that or move to transition and then adjust it later on before flower ?

@Wake I’m setting up the chiller right now, and was about to go a different route from you. feel free to let me know if you think theres some oversight with it.

My friend also got a grobo, and both machines are in the same room at the moment, so the idea is to have one chiller for both (especially since my unit, while inexpensive, is still verry bulky for the room). obviously with nutrient and ph regulation, feeding and drawing fresh water to two separate unite isn’t really an option.
So instead of having to pump and chill the tank water itself, I’m setting up a closed loop that would go through both tanks and then return to the chiller. The smart plug probe will be on the second grobo down the line since I don’t have two water loop.
not sure what tubbing I can use inside the unit yet, my initial idea was coiled copper or ss tubbing for obvious heat conductivity reason, @Stephen is there any reason not to put specific metal inside the tank ?
Also wondering if theres any time during the day when the bubbler turns off ? I’m counting on it to help the convection happens, so if it’s off, I should probably avoid turning on the chiller.


Definitely add at least a week probably going to extend again as well. No worries, seen many slow starters outgrow the Grobo so let’s see what happens.

As for a chiller I don’t recommend using one chiller for both units. Chillers circulate the water but circulates nutrients as well and the only way this would work is if both units/plants are on the exact same recipe and timing in the grow. The nutrients change based on where in the grow cycle you are so i foresee an issue if one plant is stunted and the cycles go out of sync. If you have one plant say in flower and one still in veg, that will cause problems. Hope this made sense.

As far as copper, it has natural antibacterial properties that are not good for plants. Most plants form a mini ecosystem inside a water reservoir that has natural bacteria growing in it that helps the plant and bacteria so a nice symbiotic relationship. Copper could disrupt or kill off the good bacteria while it is trying to cool down your tank.

As for a chiller I don’t recommend using one chiller for both units ... that will cause problems :

this is why I’m going for a closed loop, The idea is to have the chiller circulate it’s own water through tubbing inside the tank, making the 3 systems (2 grobo and 1 chiller) indepandent from each other.

The chiller will be on a cycle, let’s 10mn every 4h, and only trigger if tanks are above a certain temperature.

As far as copper, it has natural antibacterial properties ... plant and bacteria so a nice symbiotic relationship

Thanks, it was one of my concern, the other one would have been metal mixing from what’s inside the chiller itself. I’ll play with food garde plastic instead then :slight_smile:

Quick update from her trunk : happy to report she’s healing daily now !

I can clearly see a deep green appearing, and the wounded arrea is thick, dry and sturdy now. :partying_face: :smiling_face_with_three_hearts:Amazed by what a plant can do in 5 days !
I also extended the stage as you suggested, and topped her, I beleive she’ll be cruising now :sunglasses:


Not sure the plastic tubing will create enough transference of temperature since it is an insulator but it is a small reservoir so it may just work.