Hi Mike,

Thank you for reaching out!

Yes, the pH differences can become an issue. However, you’ll be surprised at how adaptable plants are with slightly different pH levels. The pH preferences are indicators for optimal growth but don’t necessarily refer to the range for survival. In the case of lettuce, it’s a pretty hardy crop that definitely can survive pH levels out of its optimal range.

Although yellowing leaves are often a sign of iron deficiency, I’d advise that you look out for other contributing factors.

Environmental factors are a major factor. For example, CO2 levels have a significant influence on your plant. Lighting and temperature are also impactful when it comes to leaf yellowing. In the case of lettuce, it needs good airflow in order to maintain solid nutrient uptake.

I’d advise investigating those aspects of your grow so that you can take a more holistic approach to problem-solving.

If you test your iron levels and find that they are off, you can consider adding chelated iron to your system. Thankfully, cheated iron is organic and should keep the fish, plants, and bacteria happy.

Then, of course, your water source should be checked. There have been cases where magnesium or iron is missing from the water source itself.

In summary, going back to the basic components of your system is always a great way to start the process of problem elimination. Start with the environmental elements, look at your water source, try to keep your pH at 7 (it’ll result in fewer adaptation issues for the lettuce), consider cheated iron, and maintain good airflow.

Lastly, the brief answer to your question on a pH level that would suit both: pH 7.

I hope this helps!