Slow growth rate

Hi, I have two cannabis plants that were planted in the same day (middle of April). Both are cutting . One is Purple Haze (the small one) and the second is Tutankhamun. Both are growing hydroponic (DWC) in the same condition. Electrical conductivity around 1350us/cm, PH 5.7. Growth room temperature 26.5, RH 53%. The roots look healthy in both plants. The light is 250W dual spectrum, cool tube reflector 35 cm above plant tip. Sometimes I use fan in the growth space. As you can see in the photos the small plant looks “tired” and its growth rate is slow and stunted compare to the second plant. Do you know what is the problem according to the photos and the data I wrote?

Many thanks

Welcome to ILGM!
Slow growth rate could be a lot of things. Is there enough air being forced through the air stone?
What are you water temperatures?
The other one looks pretty good, and if they’re facing the same environment, it could just be the one plant. Sometimes they just lag the whole way. I’ll tag some other hydro growers and get you some other suggestions/questions.
@peachfuzz @TDubWilly and @Myfriendis410


That doesn’t look like an electrical conductivity measurement…

It looks more like a ppm measurement and if your at 1350ppm on plants that size then you have way over fertilized and your causing massive nutrient lockout

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Are you sure your pumping enough air into your buckets

What is the temp of the water in your buckets? It needs to be below about 70 degrees for best results. Basically for every degree above 70 you need to pump extra air into the bucket

Thanks for your quick respond.
There is one air pump (with two air stones) for each plant. The water temperatures are max: 27 Min: 23
Today after work when I came to check the plants, very few leaves of the big plant also have started wilt like the small plant so I have suspicion it is the beginning of root rot. I have replaced the water and let more space left from the bottom of the cone to the water surface. Later I will put frozen bottle in the water. The root are not sticky but they become yellow /brown these is also indication for root rot. I will check in few days if I see new white root hairs growing on.

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It is electrical conductivity unit measurement. Maybe you know is as dS/m or mS/cm. Anyway the electrical conductivity is 1.3 dS/m it is not consider high and the plants have reached to this size by the same conductivity level

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Now I have added one more pump. Man, how much 70 are in Celsius?

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Your temps are too high. Like @TDubWilly said about air and water temp. Are you running any beneficial microbes like Hydroguard?

23C is 73.4F and 27C is 80! That’s WAY too high.


No, but I will try to find something similar where I live. I’m gonna add freezing bottles to the reservoir to decrease the temperature of the solution. Now the temperature of my growth space is 25 Celsius degrees, I tend to believe that the reservoir as similar temperature as the growth space . I also spaced between the tip of the cone to water surface.
Let’s hope for good news

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Yeah I should have put farenheit. Sorry about that.

Good catch @Myfriendis410 and thank you.

It doesn’t matter how many air stones although extra ones help spread the air out over a larger volumes of water. What matters is the size of the air pump.

The air pumps sold in hydro kits are normally to weak


Def check the temps and ensure you have enough air. Also not sure about the ec reading either. I had one plant that literally took weeks to root out and is now my biggest plant. Check and recheck all
Your basics, the answer is in the numbers.

Also def try hydroguard it’ll help the roots a ton.