1st time grower, dark spots on seedling

Hello everyone. I am a first time grower, and I started with 4 seeds of those 4, 3 sprouted and now 1 is showing problems.

Conditions:
Plants are around 14days old
Growing indoor
Grow medium soil
I was watering it only with distilled water.
Temperature around 60-75F (20-25C)
Humidity 40-60RH
Light cycle is 18/6. MH 250W light, plants are around 22cm (8.6inch) below the light, checked it with hand its not hot.

All plants get the same treatment, but only this one is showing these signs.

First spots were light brown, and now they are more distinct. And it shows on smaller (new) leaves at their very end. I was searching thru the internet and the only thing that looks like it is Calcium deficiency. But I might be wrong. I am getting worried


If someone can help me I would be rather grateful

you should be more concerned about your plants being yellow
are they all that yellow?

what KIND of soil are you using, usually at this stage of growth the biggest mistakes is , wrong soil, hot soil, and over watering

@sunni thank you for the fast reply. The picture was taken under the light with the flash, that is why they appear yellow. They are light green color.
I am using some recommended soil for growing. It got perlite in it, ph 6. Other 2 plants have the exact same treatment and they are not showing any signs of this brown spots.

If you can take a photo with the lights out (flash only) it will help help.

Does the soil have a brand? Does it have nutrient information printed on the bag, like 0.20 - 0.13 - 0.18 ?

Without more accurate color, I'm thinking Ca def.

What is your tap water's PPMs? (If you don't know, your city or water supplier should tell you. Or, you can buy a TDS/PPM meter. I use the HM EZ-TDS on Amazon.

Here are photos without the lights.
I was watering them only with destilled water (I used tap yesterday when I transplanted them cuz I thought previous pots were too small). And I don't have the PPMs info.

About the soil its Steckmedium (some German brand) recommended for plants. and regarding the nutrients it just says low level of nutrients 0.5g/l

Looks like problem with soil. Waiting for other answers.

The third one looks good. The first two look overwatered. The spots don't look like Ca to me (now, under balanced light. Looks like P def, but probably due to the soil being kept too wet. NPK are available at higher pH. Soil's pH rises as it dries. If you keep it wet, it limits the range it experiences.

They're planted in containers that are modestly too large. This makes it harder to get the full wet/saturated to dry/light cycle. Next time, small 18-22oz (500-650ml) containers will make it easier for you.

I googled about the soil and the first result was someone on 420mag doing a grow. It looks like the soil should work. I can't tell if he added 25% perlite, or is saying the product has 25%. It looks like the same amount as yours, so I assume the latter. (In the future I would consider adding 25%. Perlite is good stuff. Cannabis likes quick drainage, faster drying. It should dry and ready for water in 2-3 days if the plant has grown into the container.).

Distilled water has no minerals. I don't think that's your problem at the moment. Typically people use distilled or RO (reverse osmosis filtered) water and add minerals back using a calmag product. Or, if you know the EC (TDS) of your tap water, it may be sufficient. Often, tap water is too high -- that's why people use pure water. Mine is 600-800ppm (1.2-1.6 EC). I mix mine with RO water to get 150ppm (0.3 EC). That's something you should investigate. If your tap is 0.3, you could use it. If not, I would mix to get that. But, using RO or distilled by itself can be contribute to a problem later.

I can't tell if you need to start feeding. Probably not. But, you could read the other thread to see when he began. For now I think it's over watering. It should become very dry, then very wet. (But, that's hard to do if the container is too large. And, I wouldn't let it get completely dry when in seedling stage. But, people err on the side of wet, so I wouldn't worry about going too dry.).

They were at smaller container until yesterday, when I replanted them in this bigger ones because roots were comming out of the bottom and I thought that might have been the cause.
In that pot they were drinking all the water after 1-2 days. And after 2 days it would be completely dry.

I am still suspecting bad batch of soil. I think another plant will show exact same symptomes but that its early to capture with camera. :/

I am not sure if I should replant them now in the different soil. That might be too much of a stress to them.
And when I replant I will have to soak them again in water, and not sure how good will that go.

Space_Lulu said:

They were at smaller container until yesterday, when I replanted them in this bigger ones because roots were coming out of the bottom and I thought that might have been the cause.

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What size container was the first one? It's hard to believe it outgrew it unless it was an 8oz (200-250ml) container.

Just because roots are coming out doesn't necessarily mean it's time to transplant. I let mine go a little long in a container, leaves overhanging the edge. (Next time post pictures and ask if it's time to transplant. It may have been time. But, judging by the size of the plants, I don't think so.).

Space_Lulu said:

I am still suspecting bad batch of soil.

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How does this soil differ from what they grew in in the first container?

There's no good way to transplant them again now.

The first container was around that size, 300ml.
The soil they are currently in is of the same kind that was used when they were in smaller pots.
But I got different type of soil, if that is the problem. Just not sure how smart it is to replant them again. :/

Dont worry about replanting them until they are too large for their pots. IMHO i would water them once per week with 2tsp of aloe vera, 1 tsp of freeze dried coconut, 1oz of terraganix EM1, and Ful power all mixed per gallon non chlorinated water. Once they are too large for their current pot size i would transplant them to 5 gallon smart pots or any good quality fabric pots. Once they are about 8 inches high put a topping of Earth worm castings, Crustacean Meal, Insect Frass, and some good Microbes. I suggest modern microbes from build a soil. Dont worry too much about the spots right now, just watch the new growth, it should be lush and green after the a obove changes.

What I found out that the soil I am using has next to none nutrients (small amounts only) and I've been feeding the plants only with distilled water. Could that be the problem, that there is no nutriets for the plants and that is the reason for the spots and slow growth?

Space_Lulu said:

What I found out that the soil I am using has next to none nutrients (small amounts only) and I've been feeding the plants only with distilled water. Could that be the problem, that there is no nutriets for the plants and that is the reason for the spots and slow growth?

Click to expand...

Hi there , i did a similar thing with mine , i thought there was nutes in soil but found out other wise, i would recomend using root juice or some low nute rooting nutes. for about a week then start to up dose slowly and see how it gose

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Space_Lulu said:

What I found out that the soil I am using has next to none nutrients (small amounts only) and I've been feeding the plants only with distilled water. Could that be the problem, that there is no nutriets for the plants and that is the reason for the spots and slow growth?

Click to expand...

Yes. Exactly. You need very little of anything nutrient wise for young seedlings. I would quit distilled water asap. Either tap or if thats not sn option go with spring water. Distilled water also dorsnt carry the correct electical charge to aid in transfer of nutrients.