PH problems? Need advice (pics, detailed)

DWC with fox farm nutes approximately full strength (as per instructions) at week 3
80% distilled 20% filtered tap water (tap is PH 7.7, 290 ppm)
water temp avg about 71, range 68-73
air temp 71 floor, 80 canopy
PH I try for 5.6 but the range is 5.5 - 6.8 but sometimes it ranges as high as 7.5
ppm is just under 900 at the moment
lights are 6 55 to 65 watt SHO florescent lights 6700 K
air flow is more than sufficient.

Overall I think the plant is doing okay, but I don't want these leaves getting sick in veg. There are probably a total of 6 fan leaves affected right now.

I have a hard time keeping PH consistent. I changed water yesterday, PH at 5.6 next morning it was at 7. Brought it down to 5.5 using ph down and in about 2 hours it is at 6.05. So it is hard for me to keep the PH consistent, and I can't always check the water so often, so sometimes it gets way to high.

I am pretty sure the problem is PH causing lockout, but if anyone has any other ideas, I am open to any suggestions.

If it is PH, I would really appreciate advice on how to keep it consistent. Specific advice would be best also if I don't use the 20% tap the ph is 4 after adding nutes.

Thanks, and to give rep I just type "+REP" is that right?

5.5 to 6.8 is pretty much your optimal range, honestly at 5.5 its pushing low, nitrogen and phosphorus start to lock out any lower than 5.5 Locking out primaries is a big problem. Most experienced growers try for 5.8 to 6.2 as this allows for optimal intake of the mains and micros in the cannabis plant. Really you gotta dial in your strains though. Your problem does seem to be lock out related but not extreme. How long do you wait between reservoir exchanges? If your mixing your nutes and water correctly, then checking them and balancing them to the desired ph and ppm, and then adding them to your reservoir, the only thing that would immedietly affect your ph like that would be : salt build up in reservoir and or medium/roots (solution=flush and clean everything) or this http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/waterph.html

theres a difference in your tap water having a high ph and high alkalinity. If your tap is 7.7 and 290ppm then maybe its naturally high in bicarbonates and lowering the ph wont help. Trace element deficiencies and imbalances of calcium (Ca) and magnesium (Mg) can result from irrigating with high alkalinity water. Your lockout looks similar to this.

thanks for the reply, 906breeder. I think I might try using RO water from the fish store, because it should be a little harder than distilled, and maybe I can get a good ph with the RO alone....
also another thought I had was should I try mixing my nutes and water and then waiting say 12 - 24 hours before using it (adjusting ph during that 24 hours) I have noticed the PH gets more stable towards the end of the week (I change water weekly).

Also, 906breeder, I wanted to let you know that I don't use a res at all, just 3 5g buckets, 1 for each plant, so I change 100% of water weekly.

I am going to try shooting for 5.8-6.2 now. Thanks for all your advice

I wanted to see if I could get a little more advice:

Plant is looking slightly worse today (spots are spreading a little more, but still only on fan leaves). Since I am using about 80/20 distilled / tap ratio I don't really think I should have super high alk water (any alk or hardness would be 1/5 of what my tap is). I checked the nutes I am using big bloom and grow big, which has 2% Ca and .5% Mg. I think 906breeder is right about the Ca /Mg deficiencies, because pics of those problems look a lot like my problem.

So what I am wondering is should I get some cal-mag, or do I just keep my ph 5.8-6.2 and wait. How long before I should see an improvement, and how long before I should see no more new damage?

I had an issue where all my plants were healthy but leaves were weak at stem base, i added like 2.5 teaspoons of Magical and 10 teaspoons of SugarDaddy per 5 Gallons and solved it...assuming it was a Ma or Ca defin. but the sugar boost helped i'm sure. The alkalinity was a far shot but you just never know so it doesnt hurt to look you know. But defiencies are pretty easy to see and judge, its a matter of spotting them early that takes skill and pure prevention makes experts. If your becoming more and more convinced everyday that its a Calcium issue....chances are...but hopefully somebody else says something so its not just me and you sitting here talking about it.

Nice responses breeder.

I wanted to let you know about how the pH scale works if you didn't know.

PH is a base 10 system. This means that every full number is 10 times more acidic or base than its predecessor. Ex, a pH of 7 is 10 times more base than a ph of 6.

A pH of 5.8 is 100 times more acidic than a pH of 7.8

You add rep by clicking on the 6 pointed medal beneath their post. The medal is on the left side adjacent to "journal this post". When rep is received, it in anonymous. If you want the person to know you gave it, include your name as a sig. Or not, its up to you! I'll show you quick, check the bottom of your "my rollitup"

-Grizz

906breeder: thanks again buddy, I got some liquid cal and mg from the fish store. I am adding tiny amounts and checking alk (test strips) ppm and ph (digital meter) to make sure I don't over do it. I figure it will take a few days for things to sort out.

I really appreciate you taking the time to help me out. I think your idea

If your becoming more and more convinced everyday that its a Calcium issue....chances are

Click to expand...

is a really excellent one. I'll try to trust my instincts, but I would have never even thought of it without you putting the idea that cal mag was the problem in my head.

what are you using to lower your water's ph ?

I am using API ph down which is an aquarium ph down product. I had used vinegar at first, but it's been at least 2 weeks since then. I stopped because I thought it wasn't working well enough, but I found that really its more an issue with the water you use, and not so much which ph lowering chem you use. once I started using mostly distilled the swings changed from 5.5 - 8 to 5.5 -6.5. Now I am running about 5.7 - 6.3 which I think is okay.

Plant still doesn't look great, I am hoping it improves in the next couple of days. I'm not sure if I should have added the aquarium cal and aquarium mag, but I figured it was worth a try, since I only added a tiny amount.

Plant is up to 15" now and all new growth looks awesome, it's just all the large mature fan leaves show major (nodes 1 and 2) thru very minor ( nodes 5 & 6) spotting that could be either ph or calcium problems. The damage isn't quite as specific looking as a cal problem, so I still think the plant is recovering from the major ph problems I had before. But any advice is always appreciated.

I'll post some more pics around this time tomorrow.

Thanks for asking.