Heat Problem on First Grow

Greetings, my first grow and following http://www.growweedeasy.com/easiest-grow-method-cfl-coco-coir using coco and General Hydroponics nutrient with FG 2.5, FM 2.5 and FB 1.5 (they're about 4 weeks old).  Had a problem a week ago with low pH in and coming out lower, concluded pH burn from reading.  Flushed them all with 3-4 volumes of pH ~6 water, waited a few days, cut the nutrient concentration in half before I resumed watering.  Don't know what kind they are.
 
"Grow Box Nov. 3rd"

 
I built it myself from a large cardboard box with mylar I had, been closing the door so it's sealed but have a fan inside so it's been helping keeping it cool.  Have 4 x 100W 6500K CFLs and occasional supplement of CO[SUB]2[/SUB] via acetic acid and sodium bicarbonate.  I've FIMmed them all, some better than others.
 
"pH Burn"

 
So fast forward to Friday.  Back to regular strength nutrients and feed them a little, ~100 mL.  Yesterday they were looking good so fed them the rest but didn't add much CO[SUB]2[/SUB], forgot.  12 hours later this morning I check on them.  Note when I opened this morning it was very humid and hot.  Slowly collecting other necessities, but no temperature, humidity, CO[SUB]2[/SUB], or salinity probe.
 
"Grow Box Nov. 10"

 
Obviously they've really started to take off so I'm not a complete idiot, but it appears they now have heat stress.  Doesn't appear to be pH problem.
 
"Gen. 1B"

 
All generation 1A's died, I planted them in Miracle Grow.  Next plant Gen. 1B, I used coco and GH, I think I was still not correctly checking the pH, getting it around 5.0 - 5.5.  Only one survived.
 
"Gen. 1C"

 
Next plant a week later, 5 of 8 have survived.  All leaf tips are curling up and sides bowing up.  Some brown discoloration and drying, but nothing like the whitening I saw last week and mostly on the leaves that were affected from last week.  However I tested the pH of the flow through and it's coming out around 8 when a few days ago it was 6.  I've checked my nutrient solution several times, washing the vial and dropper to make sure no residues are affecting it.  It comes back yellow which means pH of 6.
 
Really can't afford to start over.  I'm growing for medical reasons; broke 5 vertebrae in my back and neck earlier this year and apart from the horrible pain I go days without sleeping and eating.  
 
I've propped the door open 15 cm and added a lot of CO[SUB]2[/SUB].  Figured from what I've read high CO[SUB]2[/SUB] helps when temperature and humidity are high, or at least all three have to be high in order for there to be benefit.
 
Thanks.

 

Closest thing to a form I could find.
 
What type of medium; soil or hydro?
-Coco
What brand and type of soil?
-Kempf, washed with 5 volumes size amounts of pH 6 water before using to flush out salts.  4 parts coco, 1 part perlite.
Indoors or outdoors?
-Indoors, cardboard box lined with mylar.
What strain?
-No idea, appears sativa dominant.
How old are the plants?
-4 weeks.  Seeds sprouted very quickly after planting.
What type of lights and how many watts?
-4 x 100 W CFL, 6,500K.
How far from the lights?
-5 cm at the closest.
What is your watering frequency and source of water?
-Generally every other day, 200-300 mL, soft water faucet that comes out at a pH of 6.
What, how much and when was it fed? NPK?
-General Hydroponics: 2.5 mL FloraGro (2-1-6), 2.5 mL FloraMicro (5-0-1), 1.5 mL FloraBloom (0-5-4).
What is the medium/runoff pH and PPM if in hydro?
-8 (was 6 til I fed them yesterday), no way to tell PPM.
What are the temps and humidity in the room?
-~30 ºC, can't tell humidity but my guess is +40%.
What size pots?
-2.66 L
Any bugs? Look real close.
-None that I can see.
Any other pertinent info?
-Thinking I may have added 2.5 mL of FloraBloom and 1.5 mL of FloraMicro instead of the other way around, didn't seem purple enough.  Though don't know why that would explain a higher pH coming out than going in.  Occasionally add in CO[SUB]2[/SUB] via acetic acid and sodium bicarbonate.  Didn't add any last night.

 

 
No choice in the matter, person I'm living with "has to have" soft water.  After I flushed them last week with just the water from the shower they seemed to recover from what appeared to be pH burn and were really taking off.  Was giving them half of the nutrients of what I listed so I guess I'll go back to that.  
 
Just flushed them again and the run off has a pH of 6, don't know how it shot up to 8 when I fed them with nutrient water with a pH of 6 last night.  The light has been constantly no closer than 5 cm and some that are farther away (20 cm) have the "canoeing" while some at 5 cm don't have it.  When I water with nutrients I make sure that the top few centimeters are dry.  Know overwatering can be a problem for beginners so I do my best not to.  Going to start leaving the door always open to let the heat escape.  Guess I can axe my CO[SUB]2[/SUB] soda method.

 

 
Yeah, sorry.  I'm American but spend so much time only using the metric system it's my default.  Getting ready to hang them from the top of my "grow box" because they're getting too tall.  They're around node 5 but it's hard to tell because the nodes are so close.
 

 
I'll look into it.  I flush them with a removable shower head and fill my water pitcher with water from the sink faucet, see no reason why one would be soft and the other hard.
 
EDIT:  Roommate actually grew a 3 foot plant on the balcony with the same water in Miracle Grow.  Didn't look anything like mine in terms of bushiness because he didn't FIM.  Nodes were 2-3 inches (5-8 cm) apart.

 

The leaves seemed to have stop "canoeing" but I lost a lot of leaf area to the rolled-up edges dieing.  Fed them with ~100 mL of the half nutrient solution.  Most of the new growth at the top doesn't seem too affected, clipped off most the dead leaf spots so that more light can penetrate.
 
Plants would probably be a lot bigger if I could find a way to stop screwing up every week and retarding their growth.

 

 
The only real thing I think I've done well on so far is keeping the nodes short.  Most have a node-to-node distance of 1 cm and the stems are pretty strong so they should be able to take some weight.  Once they get large enough I'll probable string together a net system once I switch them over to flowering.  Considering my need, that'll probably be once they reach a foot or so.  
 
Thanks again helping.

 

~3 weeks update.
 
FIMed 3 about a week ago because once I stopped screwing-up the non-FIMed ones really started to grow tall and don't want them to outgrow the box.

 
How much can I expect them to grow during flowering?  I'm going to switch them next week when the new growths from FIMing become a little more like the FIMed one on the bottom left which I did 2 weeks ago.  I've read sativas, which there one appears like it is more sativa, can grow 2-3x in height because flowering can take several months.
 

 
Back right and center I'm really hoping turn out to be females.  Smoked a few dried out leaves and got a very small buzz so will probably look into making hash with the males in a few weeks.
 
Back Right:

 
Center:

 
Thanks again.

 

Well damn.  Looks like I stressed them into hermaphrodites.

 

Thanks, turns out only one was stressed into a hermie, so I still have 3.  One is looking very nice and can see a lot of white hairs developing, the other 2 are pretty ugly and I don't expect much from them.  No smell as of right now, though rubbing my thumb and forefinger on the stalk up-and-down makes them smell   Did cut some holes from the top to allow heat to escape and hung some lights, now have 6 x 23 W.
 
This is my favorite, it's been in flowering for 2 weeks.  Some leaves are missing from the bottom because I let it dry out over Thanksgiving when I was gone.  Hoping for an ounce out of this.