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"The pH was high (7.5 or close to 8)..."
Nutrient solution pH outside the range of 5.5 to 6.0 makes vital nutrients unavailable to plants and can indeed cause the issues you are experiencing. Think of it this way (analogy): Starving to death in the middle of a grocery store because the food is up on a 20 foot shelf and you have no way to reach it (a pH of 5.5 to 6.0 is a guy handing you a ladder).
"I adjusted [the pH] back down..."
Abruptly altering the nutrient solution pH from ~8.0 to ~6.0 in less than 24-48 hours would definitely contribute to the poor condition of the plants. It's all about BABY STEPS. You should never add more than 2 tsp. of pH adjuster at a time... and wait a minimum of 30 minutes between adjustments (even that is a bit aggressive when you are making such a large change in pH as you did). FYI: pH is a logarithmic scale (just like the earthquake Richter Scale). This means 8.0 is 10 times greater than 7.0... and 8.0 is 100 times greater than 6.0 and 8.0 is a 1000 times greater than 5.0 - little numbers make a BIG difference... and plants are VERY sensitive to abrupt changes in pH.
"I have returned a couple weeks later..."
Has the customer been properly maintaining the TG during your absence (for just one example: performing regular tub top-offs with fresh nutrients)? If not, toss this on the pile of causes for your issue.
"The air temp is close to 90 during the summer months..."
Ambient air temperature can run a little warmer provided you keep the nutrient solution temperature in the critical 65°F to 75°F range. If your customer has not been keeping the nutrient solution temp in this range then you can toss yet another cause on the pile. In addition, nutrient solution temps over 75°F provide an optimal breeding ground for a host of undesirable plant diseases and pathogens. Things basically start to spiral out of control with nutrient solution temps over 75°F.
Typically, "leggy" implies "not enough light"... However, you have so many other bad things going on here it's difficult to say for sure. "Leggy" in this case could very well be a symptom of the other issues I noted above.
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