I'm starting tomato seedlings. Used a seed starting mix. They've been fine up until about a week ago. Started about 3 weeks ago. I transplanted them into 4" pots from 2" peat pots about 3 days ago. I have fluorescent lights on them 3-4" above. Lights are on 16 hrs/day.

I've had a heating mat under them from day one, and I just realized it might not be a good idea to have it on now. The room temp has shot up to 80 degrees due to the heat we've been having here. I water once a day, they are usually almost dry by that time.

From what I've seen on the web, this seems like Phosphorous deficiency. However, the temperatures are definitely not cold. If anything, they might be too warm.

I'm concerned that I might need to fertilize it. I have a 4-4-4 organic fertilizer which I'm currently making a tea out of. Not sure if this will be fast enough to act, as I read that they take time to work.

Any advice?

My "Cherry Roma" tomato:

Here is another tomato ("Gold Medal"):

Thanks in advance.