Well first i'll say that this is my first time growing.
This plant is about 5 weeks old I water it normally started it in a half of a 2 liter bottle i cleaned let it sprout do it's thing all that. It was growing quick so i switched it to a 20 gallon aquarium. It has grew no problems at all just perfectly too perfect..

Now the problems

1.A few of the leaves started drooping a few days ago and are starting to get a yellowish color to them alot of the leaves are starting to die.

2. Around the top few leaves they have a web going from the stem to them looks like spider web almost today I found 1 tiny black round bug crawling down the stem i picked it off and killed it and have searched and found no more bugs.

So my main thing is what is wrong with it?

Could be anything - sounds like you need to start feeding it some nutrients or it could be watering problems.

20 Gallon container?

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Mandala Seeds Kalichakra and Satori Grow
Holefillers 0.6gram per watt 64w Micro Grow

the spider web is from spider mites, they can wreck your plant. Go to walmart and get a plant safe 3 in 1 fungide, spidermite and other insect spray, this will keep them away. Also pull the webs off the plants when you see them

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i do not grow marijuana in any way shape or form

Ok I kinda thought it could've been spider mites guess im wal mart shopping tonight. thank you.