I need some help guys and girl

[Manuelnoyes]

Most of my lower leaves are turning yellow and getting brown spots I don't now how to fix this problem I'm almost 3 weeks in to flowering and I need help

 

[OzBud]

Could possibly be a phosphorus deficiency?
http://www.growweedeasy.com/phosphorus-deficiency-cannabis

Are you giving any nutes?
Are you checking pH?

 

[Manuelnoyes]

I am giving them fox farm tiger bloom and have phed the water and nutrient solution ever time I'm starting to wonder about fungus gnats but this is only one of three plants

 

[OzBud]

Do you ever check runoff water pH? Even if it's going In at the right pH depending what's going on in the growing medium with excess leftover nutes, salt buildup etc the actual pH in the soil could be off preventing your plant from accessing all nutrients.

 

[Manuelnoyes]

I haven't in a while I'll check tomorrow after I water

 

[NebulaHaze]

If you have a bad fungus gnat infestation, it can cause symptoms like the following. If you have fungus gnats, chances are you're watering your plants too often, and the top inch of soil is staying wet for long periods of time. That's where fungus gnats lay their eggs, and the larva need wet topsoil to survive.

However, from the pics it almost looks like you have a Calcium deficiency. Are you using soft/RO water or growing in coco coir? If so, it's highly recommended to get a Cal-Mag supplement to help prevent Calcium deficiencies.

I also second the idea of checking the pH of the runoff water. If you're putting it in at 6 and it's coming out at 5, you'll know the pH may be causing your problem, since it's the most common reason to see deficiencies

Is it possible to post a picture of the plants in the setup from a foot or two away, so we can see the whole thing? Sometimes being able to see the whole plant in the setup can make things easier to diagnose