Diagnosis Needed...and Solutions Welcome

Hello All,
This is my first grow and I'm having an issue, though it seems somewhat minor. I have two plants and both seem to be exhibiting the same problem. It may simply be nutrient burn from overdosing the plants early on and mixing miracle grow into the soil mix. The mix, btw, is enriched potting soil, sand, pebbles, and drainage moss. I've flushed them a couple times and new growth "seems" to be doing okay, but if it continues I want to have a solution ready.
The problem: Older leaves burn at the tip, curl under, eventually die.
I attached pics; the yellow leaf was taken off the large plant near the bottom.
My suspicion is Potassium deficiency, possibly cause by nutrient lock out. However, the soil pH is about 6.8 - 7. So maybe I just need to add more potassium. The last couple days I've tried foliar feeding with mild nutrient solution when the lights are off and the plant is cooled. No real change yet.

Any ideas, advice, tips, etc?

Thanks

the little one looks a lil over fertilized....u say u flushed it,so use water til u see the burning stop
the big one looks like a N def....maybe some P def on the back leaf.... but reguardless u need to mix ur nutes a lil stronger

I'm not an expert on the subject, but it seems if you use miracle grow, do not add any nutes for the first 3 months, which might mean no nutes for the entire grow.

Nutrient Burn. Flush them with clean water

Thanks for the feedback all. I'm hearing opposing views so I'm wondering if you tell me how confident you each are in your diagnosis, and maybe what in the picture leads you to your conclusion.
Here is a little more info. The large one got the miracle grow added whereas the little one was planted more recently and without nutrient added. Prior to planting though, it did get foliar nutrient. The little one hasn't needed to be flushed as a result. The big one has done better since the flush, done 3-4 weeks ago.

emanym said:

Thanks for the feedback all. I'm hearing opposing views so I'm wondering if you tell me how confident you each are in your diagnosis, and maybe what in the picture leads you to your conclusion.
Here is a little more info. The large one got the miracle grow added whereas the little one was planted more recently and without nutrient added. Prior to planting though, it did get foliar nutrient. The little one hasn't needed to be flushed as a result. The big one has done better since the flush, done 3-4 weeks ago.

Click to expand...

if the little one was only foliar fed and is not getting worse,then it should be fine
as for the big one...the yellow leaf is clearly a N def...and on the 2nd pic,the back leaf looks like its burnt like a P def.....reguardless whether its a P or N def,it is deficient in nutrients and needs more
its what i would do if they were mine,i feel confident on this
good luck

I am not used to miracle grow but I do know this every time you water them they are getting nutes from the miracle grow. It is a something that already has high PH factors. Let the plant COMPLETELY dry out like 2 1/2 to 3 day between waterings. One of the most common things I see is overwatering and it in turn will lead to nute burn. Heads up pick the pot up and you can tell if it still has water. Experts will tell you the more often the plants dries out the better so if you gave them just a touch 1 time a day they would be fine but if you give them say 5 seconds of watering you want to water every 2 days. 10 seconds and you wanna water every 3 days. Hope it helps.

I think there's some confusion here regarding the MG- I'm assuming your using MG fertilizer, not MG potting soil/mix????? Soil pH meters are shit- throw it out. You need to pH test your water with ferts going into the soil and then if problems arise, check the water leaving the pots. pH in should be around 6.3. pH out should be higher. Problems this early will typically run thru out the grow, especially when they are varied like yours. I see a couple of different issues going on. MG ferts are full of heavy metals in the salts- a poor choice for marijuana growing and typically not a complete fertilizer. Buy something made for hydroponics. Lastly, and my best suggestion: newbies should grow an easy indica strain their first couple grows to get the hang of it. So often I see a new guy trying to grow a haze hybrid or a NYCD. Try Northern Lights or an Afghani and it will go much better for you. It's easy to get frustrated and start over correcting making things worse.......