Yellowing Leaves After Swith To Bloom - Pictures Included

[GrowerXLT]

Some of the leaves on my plants began to yellow about two weeks ago. The progression appears to start with small yellow dots, then the tips of the leaves yellow and the tips of the leaves curl down. I first noticed a couple days after the plants were switched over to flowering which also means I changed the nutrients to flowering nuterients (General Hydroponics - Flora Nova Series).

The water being used is RO with a ppm of 3, so, I added enough nutrients to get a 10 gallon hydro system to 450 ppm. My first instinct is to think the problem is nutrient burn.

However, I have been using neem oil, (diluted w/ soap and hot water) to deal with any potential pests. I began the neem treatment about a week before the plants were switched from veg to flower. I read that the plants need to be sprayed with water following the neem treatment, so I have been spraying with my neem mixture one day, and water the next two days, and have been doing this for close to two weeks now. The neem treatment appears to be working as far as keeping pests under control, but being new to this I am not really sure, and I am also not sure if it is what is damaging the plants. Here is the link to the neem process I am using:
http://growfaq.marijuana.com/growfaq/1667.htm

After a week, I changed out the water and added only enough nutrients to get the system at 175 ppm as opposed to 450ppm as I was using the previous week hoping that this would solve the problem. However the damage appears to be continuing. Any feedback would be helpful, and if anyone needs more details please ask.

Setup:
BC Northern Lights - Producer - 2x430 Watt HPS
http://bcnorthernlights.com/?page=home

Strain:
White Widow from clones.

GrowerXLT Reviewed by GrowerXLT on 06-24-2006. Yellowing Leaves After Swith To Bloom - Pictures Included Some of the leaves on my plants began to yellow about two weeks ago. The progression appears to start with small yellow dots, then the tips of the leaves yellow and the tips of the leaves curl down. I first noticed a couple days after the plants were switched over to flowering which also means I changed the nutrients to flowering nuterients (General Hydroponics - Flora Nova Series). The water being used is RO with a ppm of 3, so, I added enough nutrients to get a 10 gallon hydro system to Rating: 5

[GrowerXLT]

Here are some photos from 06-16-2006. 5 Days Info Flowering. At this point I was using General Hydroponics Flora Nova Bloom Nuterients at 450 PPM and had spayed the neem mixture 2 times. Also I check my ph every other day and keep it between 5.5 and 6.0.

What is causing the yellowing?