Really need some help with my babies

Let me start off with some info on my grow:

Light:Outdoors
Strain:Master Kush
Water: distilled / tap* see below
Week: I think my plants are 5 weeks old sine they broke the surface.
Soil: An organic sterile potting soil with a med. amount of organice time release ferts.
Pots:2 gal. plastic pots with pete moss at the bottom for drainage.
Ferts: Have not applied anything to the plants yet.
Ph: 5.0-5.5* see below

Ok, I have 7 seedlings going in pots outdoors. Out of the 7, 1 is by far the largest, then another is a close second, then the other 5 are all about half the sice of those 2. They are all small considering they have been out there growing for 5 weeks. The biggest being about 11" and the smallest 5 all being only about 6-7" Also the smaller ones are all a much darker green and much less developed. The biggest one is much lighter green than the rest also.

I think I may be getting a pest problem due to some small brown spots on some of the leaves, and some minor blemishes.I felt it might be a Ph problem or nut problem so today I bought some neem oil, superthrive , and one of those 10 dollar Ph/moisture meters , the ones with the 2 metal prongs.

Now, using thise cheap Ph meter I tested all the pots , my tap water, and my distilled water.

My pot Ph in the bigger2 plants was about 5.5-5.7, and the other 5 smalller were about 5.0-5.3. From what I understand I need the pot Ph to be between 6.5-7 right?
My tap water: 4.5-4.9
Distilled bottled water: about a 7.5

First off-can I trust my little 10 dollar Ph meter?
second - Does too acidic conditions ( lower Ph ) seem to explain why the plants are so small for their age?

DO I need to buy some Ph up to put into my water to keep the pots where they need to be?


Any help would be appreciated!

I don't think for 5 weeks 11 inches is that small depeding on internode spacing.

shamegame said:

First off-can I trust my little 10 dollar Ph meter?
second - Does too acidic conditions ( lower Ph ) seem to explain why the plants are so small for their age?

DO I need to buy some Ph up to put into my water to keep the pots where they need to be?

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With regards to your cheap ph meter, I'd be open minded about what results its giving you, it's not 100% accurate but probably enough to give you an idea.

No, I don't think the ph has had an impact on the size of your plants.

The first thing I'd do if I were you, is repot them out of that compost with time release fertilisers into some without.

Compost to a large extent is self buffering ph wise. What that means in practical terms is that it's going to make an awful lot of either alkaline or acidic irrigation water to move the compost ph either way. You seem to have managed it though! A water ph in the 4.x's is low and fairly acidic. Composts start out at anything between a ph of 6.0 - 7.0, so it's moved into the 5.x's with your acidic water. You ought to be shooting for a soil ph of around 6.2-6.5 ideally, so 5.x is a little low although still acceptable.

You have two choices.

Option 1
Repot your plants into some non-time release fertiliser compost and mix in about a level teaspoon per litre (or 4 level teaspoons per gallon) of dolomite lime in with your compost and mix well. This will raise the soil ph nearer to neutral 7.0 and will ensure it never goes above 7.0, this will also help with your acidic irrigation water moving the soil ph, as lime is a very good ph buffer.

Option 2
Repot as above omitting the dolomite lime, but use ph up to raise your water ph to between 6.2 - 6.5. You'd need to get an accurate ph meter for this and do it each time you water.

If it were me, I'd go for option 1.