The brown/red/pink coloration that you noticed is a reaction of plants to lots of light. Only you can decide if it is too much light or not. Many ppl are trying to color their plants red.
You might want to increase the NO3 level to 10 ppm, while having an eye on the phosphates. With more NO3, plants will be greener. Low NO3 levels bring out the reds very well.
You can get PO4 test kits for example @ Marinedepot.com or BigalsOnline.com etc.