New Setup W/pics Advice Please!!!

So I have posted a couple sets of pictures on here since I started on July 4th. I started with 14 peak 19 seeds from one of my local dispensaries. I recently moved my plants to 6'' rockwool cubes and put them under the MH 400W light setup with 2 small fluorescents mounted on the sides for extra lighting. I quickly realized I needed a better grow medium and decided to take a trip to my local hydroponics store. I picked up a 6 plant setup (as this was all I could afford) picked what I thought were the 6 best plants and came home and set it up. Since I setup the hydro system the plants have quadrupled in size in only twelve days. Right now the plants are being watered two times daily for 15 minutes each time. I am using Foxfarm grow big nutrients and the temp is 74 degrees at all times. Now, I have a couple of questions for all of you experts out there... **How often do I need to change the water in the reservoir? I have 15 gallons of water in there mixed to the specifications on the back of the Foxfarm grow big nutes. **I didn't happen to get a picture of it but some of the newer leaves near the bottom are curling up and a few of the larger fan leaves are browning on the tips. Any idea what might be causing this? and, if so any suggestions for a fix? Hope the pictures are good enough for you guys to help me. I also welcome any sort of criticism and/or shit talking as this is my first grow and I didn't expect everything to go perfect. Thanks in advance guys for all the help.

IMG_0842.jpg - Image - Photobucket - Video and Image Hosting IMG_0845.jpg - Image - Photobucket - Video and Image Hosting IMG_0846.jpg - Image - Photobucket - Video and Image Hosting IMG_0849.jpg - Image - Photobucket - Video and Image Hosting IMG_0839.jpg - Image - Photobucket - Video and Image Hosting IMG_0840.jpg - Image - Photobucket - Video and Image Hosting

Sorry for the disorganized pics guys.

Please comment guys I could really use the help.

change the water every 2 weeks

try using a little less nutes when they are not that big. like 50% strength

looks like you don't need much help man!!! a very nice set up remember to keep the 400w MH At least 20 inches from the plants, one of your plants looks a bit stretchy

Try like this!
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Here are a couple more I just took. I added 2 CFL's to either side as some of the plants had small shady spots near the bottom. Also added the long Fluorescent at the back and put up a white sheet in order to keep in some of the light since the plants are setup basically in the middle of the room. TM21 I'm not sure what you mean by try this with a pic of my plants?

http://i204.photobucket.com/albums/bb319/trueword33/MOT7-29-07/IMG_0859.jpg

http://i204.photobucket.com/albums/bb319/trueword33/MOT7-29-07/IMG_0858.jpg

http://i204.photobucket.com/albums/bb319/trueword33/MOT7-29-07/IMG_0857.jpg

http://i204.photobucket.com/albums/bb319/trueword33/MOT7-29-07/IMG_0856.jpg

http://i204.photobucket.com/albums/bb319/trueword33/MOT7-29-07/IMG_0854.jpg

Also included a pic of the small brown tip of one of the plants. If anyone happens to know what might be causing this, that would be great a few of the plants have it and don't know if I should be concerned.

One more question...how much light is to much?