Flowergirl -

How long your SIL was growing and what has changed in her environment?

Water - may be the city is changing a desinfectant from chlorine to chloramine? fertilizer? distance to the lights? lights? - may be she got new tubes? Is it too cold?

Change of the color is usually a culture problem, not bugs.

Good luck to you and your SIL

Irina

Yellowing leaves could be caused by:

Too much light

Too much fertilizer

Not enough fertilizer

pH problems

If the plants are getting around 12 hours per day of light that would not be too much. More for an extended length of time could cause yellowing.

Water pH or soil pH could be the problem. You can get test strips in some nurseries, Walmart, etc.

If she could just eliminate each of these, she will be able to find out what is causing the problem.

Nancy

I'd check the fertilizer first. Could be too much or too little, more likely too little.