Do you have a soil ph meter also? I didn't see it mentioned.
I would go buy cheap distilled water, check ph, and make sure your plant has enough food. If you're not feeding it at all having the new light upped it's growth tremendously and it's needs for food and water. Go to a grow shop and get a quality nutrient for soil that contains all the micronutrients.
Only use half strength nutrients until the plant looks better.
Also I would flush the pot. Best way to do that for sure is to use a rubbermaid tub or something full of water (clean that you ph'd and let sit, or buy distilled water several gallons.)
You can slowly submerge the whole pot in the tub and let it completely fill every nook and cranny and it'll make sure there are no dead spots that don't take water normally. Then when the pot is submerged a couple inches below the water and air bubbles no longer come up for a minute or two then pull it out and let the water drain back to the large tub. Do that twice.
I always just use tap water for this that I've ph'd and let evaporate but you can buy a big jug of distilled water cheap or several gallons. Many stores have those water vending machines and if you bring your own gallon jugs it can be as cheap as 15 cents a gallon. You just need to ph it then and you're sure it's been filtered. The machine will say on it what process the water has been through.
That is also THE BEST way to water you plant every time during heavy flowering or heavy vegitative growth as long as your soil mix has good drainage. If not just do this a couple times per grow. Always let your pot go fairly dry before watering again. A little droop on the leaves and light weight to the pot is your indicator it's time to water again.
You can fill the tub with nutrients to the correct amount and it's like a manual ebb and flow in that it completely wets the soil and then when it drains it pulls fresh oxygen in. It also prevents salt buildups if you flush twice that way. You can do all your plants with the same tub if the tub is large enough and has lots of water to dilute the crap it's flushing out of the soil, but if the tub is smaller then let the plants drain into another container and check ph of the good dip tub between plants if you're doing a lot of them. You can do the soak as long as 15 minutes if you really want to be sure you're getting a full flush or if your soil is very compacted or poor soil and absorbs water slowly. If it is slow absorbtion bad soil with bad drainage a little bit of soap in the water (natural without antibacterials) will make the water wetter and let it get in hard areas much better.
It is a bit messy when lots of soil and pearlite floats out of the top of the pots but that's ok, it's worth it. If your mix is very light or the plants haven't begun to fill the container with roots then you have to dip really slowly so the dirt doesn't all just float out instantly.
Also make sure your temperatures in the grow space didn't skyrocket when the new light was put in. You need to check it after it's run for many hours with the door closed and check it fast before having the doors open for a while cools it back down. Don't sit there fussing over the plants and jerking off and then look at the temp. Check temperatures at the top and bottom of the plant, it can be a huge difference if it's a tall plant and cabinet.
I wish I knew who to credit for this watering method but I think it was dr. greenbudgenes or something like that. It was one of the very successful old timers with proof to back it up. Anyway you will see an AMAZING change for the better and when the plant is healthy and you do this then growth will be greatly sped up provided all the other conditions are good.
