Diagnose this problem || First Outdoor Grow

Hello,

I am a long time lurker, first time grower.
I have tried to do as much background information as possible and also on the fly research to tackle problems as they come up however this one is a bit out of my league and it would be great to draw on some of the experience that is around here.

The plant was fairly healthy up until today when the leaves began to curl and shrivel indicating it was one of the following variables that have occured since yesterday:
a) I watered the plant with Ph-down (more than usual) yesterday
b) The temperature today reached 37c (hottest it has been)

More info a) When I watered yesterday I used Ph-Down to correct the tap water from 7.8ph down to 6.0ph (the RO was indicating 7.1-7.2ph previously)
This was the first time I used this much Ph-Down and it seems likely that it has caused the damage.
(My recent research indicates that Ph-Down isn't a great choice for soil - I am now considering using Peat Moss, Saw Dust or Wood Chips to decrease the Ph.)

More info b) All 3 plants were in the sun (all day - but it was overcast from midday onwards) yet only this plant suffered the damage.

Diagnosis: My running theory is the Ph-Down was a bit too acidic for the plant and that began causing the leaves to taco and while it was in a weakened state the sun was too strong for it and caused damage that it had not to the other plants.

Treatment: In a somewhat knee-jerk reaction I googled the possibilities, flushed it with 30 litres of water Ph'd to 6.8 (RO was 7.3ph) and then feed it nutrients mixed 5ml/5L.

Plan: My plan now is to let is recover, allow it morning sun up until midday if it starts to get hot and then keep it shaded.

Suggestions: If anyone can confirm my suspicions or give me a corrected view that would be greatly appreciated

Problem plant:
As I can't upload pictures right now - I will try to describe it in more depth:
This morning the newest (sugar) leaves were tacoed, deep green and looked like they contained alot of water.
This afternoon some of the fan leaves have shriveled their ends and turned over.

Apologies for pictures not uploading I am missing 2 likes and need to exceed 1 day of membership. I will upload once this occurs

If you get a good balanced organic soil going, it buffers itself, I threw my meter away years ago and haven't had an issue since,LOL I still actually have one but I only monitor with it. Ph up is lime ph down use liquid sulphur, citric acid works too.

Sounds to me like you are overcomplicating a very simple thing.
Keep it simple man.

Redeyefrog, I absolutely would have gone with an organic soil however these actually started their lives indoors (until I realised it was too much of an uphill battle to keep cool in summer in a garage).
That being the case they are in a coconut husk blend (which while not ideal) is what I'm working with currently.

That is probably so, yet I still need to address the issue at hand...well I may have already but it couldn't hurt having more minds weigh in on what's going on.

(Pictures now attached)

Nute burn with good soil you don't need much nutes and skip nute feedings every other water or every two waterings