How old are the seedlings? If they are less than a week old (even out to 10 days), you really don't need to use nutrients. They will thrive on water alone.
Since you said the older leaves are showing yellowing, I am guessing these seedlings are at least a couple weeks old. I have been running a pH around 6.0 and a ppm close to 2000 for four weeks on an ebb and flow system, yet I have seen very little nutrient burn on my plants.
Also it may not be nutrient burn that you're seeing. Nutrient burn, as described in Greg Green's book "The Cannabis Grow Bible" is like a smoked joint where the tips of the of the leaves will actually looked burnt.
If you are seeing yellowing of the tips of the older leaves, you may have a nutrient issue. Nitrogen deficiency causes a yellowing at the base and creeps its way up, but the leaves do not curl up.
Magnesium issues start at older leaves first and show yellowing while the leaves will curl upward.
Hope this helps.
Since you said the older leaves are showing yellowing, I am guessing these seedlings are at least a couple weeks old. I have been running a pH around 6.0 and a ppm close to 2000 for four weeks on an ebb and flow system, yet I have seen very little nutrient burn on my plants.
Also it may not be nutrient burn that you're seeing. Nutrient burn, as described in Greg Green's book "The Cannabis Grow Bible" is like a smoked joint where the tips of the of the leaves will actually looked burnt.
If you are seeing yellowing of the tips of the older leaves, you may have a nutrient issue. Nitrogen deficiency causes a yellowing at the base and creeps its way up, but the leaves do not curl up.
Magnesium issues start at older leaves first and show yellowing while the leaves will curl upward.
Hope this helps.
