i have a problem... and its yellow

yoooo, alright i have some plants, and they were doing good for a while, a couple days ago the older leaves started turning yellow, so i thouht it was a nitrogen deficiency, ( i duno if thats right or not) so i thought the only way to fix it was to give them lots of nitrogen the next time i water them. i got some new plant food which was 20-30-20, and nothings happened except the yellow has gradually gotten more intense. if someone with some expert knowledge could help me out and point me in the right direction thatd be sweet. uh... the temp is around 74 and humidity around 45, theres tons of air flowing through my setup but i dont have a ph or tds meter so im thinking thats also my problem.

You shoudl try and keep track of the pH of the grow medium, and be sure it rests around 7. Also, during vegetative growth, you'll want more Nitrogen (N) than Phosphorus (P) or Potsassium (K), potentially 2:1:1, respectively.

yo thanks for replying to my post, what would be an easy way of testing the pH of my soil? probably getting a soil test kit from wal mart er something right? and by looking at the pics of my plants do you think they have a nitrogen problem?

Do you test your water before watering your plants? You should add your fertilizer first and then ph test. Do you have a moisture wand? They are a great help so you don't over or under water your plants. What is your max temp and your min temp. There should be a high and low. Do you need to transplant? They can start to look that way when their roots are getting crowded. Remember you need to keep your ph level at the correct level. That is very important. The kits are cheap. So get one.