The fact is that all potting mix becomes more acidic with time. (It happens.) Perhaps something else is going on.

One question that comes to mind is how long have they been in that pot?

And what do the plants/leaves look like which "are having a hard time with magnesium?"

To tell the truth, you're tossing so much stuff at those plants that it's difficult to know what's happening.

Pictures would certainly help us understand what you see. Can you post pictures?

skip the peroxide and miracle grow, add finely crushed eggshell

Bill

"The fact is that all potting mix becomes more acidic with time. (It happens.)"

I don't know anything about potting mix, so I'll accept that this is true.

But I don't understand why watering with tap water would make poting soil more acidic, but make lawn, garden and farm soil more alkaline in arid areas. I thought the reason my soil is alkaline is that it's sort of a closed system. Wouldn't the same hold tru for a potted plant (maybe more so)?

Depends on whats in your water I would imagine...

Milk is an acid also, people who can't drink milk are often actually intolerant of lactic acid.

How long have your plants been in their pots? What I mean is how long has it taken you to get to this condition? Figure it will take an equal time to get back out if you don't want to shock your plants to death. I've put baking soda in to raise ph before and it didn't kill anything. Not much though, do this slowly...

My plants have only been in the pots for maybe 4 months. I know it seems like Im throwing a lot of stuff on them, but I've only been adding it in very small amounts. A splash of very diluted fert/seaweed in with the water every couple of weeks, 1/4cup of 3% peroxide to a gallon of water maybe once a week, and only I added 2 tablespoons of epsom salts a couple of days ago.

I don't have a digital camera, but this is exactly what the lower leaves look like on my soybean plants

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Shoot, I can't edit.

bpgreen, I don't know if the city tap water is making it more acidic or not, I was just throwing out there everything that's touched the plants. :)

Irrigation water can definitely make a container soil more alkaline or acidic. Alkaline water seems to be more common in arid regions. This happens much more quickly in a container than in soil.

bpgreen's diagnosis is very sound. The leaves show to have classic micronutrient deficiency symptoms, and this is usually caused by alkaline soil. A lack of micronutrients in the fertilizer could also cause this.

Attention all:
Please note that the post with the photo said "I don't have a digital camera, but this is exactly what the lower leaves look like on my soybean plants"

So that's not kalika's plants.

So, kalika, why are you growing soybeans in a pot?
And are they indoors or out?
And what sort of temperatures are they currently receiving?

Beyond that, fresh potting mix plus fertilizer according to directions during the following 4 months, should not result in problems similar to those shown in the picture.

What else is going on? (Perhaps a blow-by-blow description of what you planted, and how would help us.)

Lacking that, can you take a plant (if potted) or a substantial-sized sample to a local independent garden center or to your county's Extension Service office?

"So that's not kalika's plants."

Right. But if the leaves on Kalika's plants look just like those, then the soybean leaves are chlorotic, just like the leaves in the photo. They look like they're suffering from a lack of iron. The most common causes of iron chlorosis are low iron levels in the soil, high pH or too much water. Of these, I think the most likely is high pH.

Repot, wash off the roots and use new soil. Check with growers of the specific plants to see if you can find recommendations for potting soil mix for that plant.
Repot, wash off the roots and use new soil. Check with growers of the specific plants to see if you can find recommendations for potting soil mix for that plant.

You are trying to manipulate a very difficult medium.

Professional growers would never try all of the things you are attempting.

You are trying to manulipate a very difficult medium.

So, kalika, why are you growing soybeans in a pot?
Because that's all I can grow in, I don't have a yard.

And are they indoors or out?
Outdoors, on the balcony.

And what sort of temperatures are they currently receiving?
100 degree days, 75 degree nights, heavy rain every few days, but not nearly enough to stop using tap water.