I have zonal geranium plants in pots in full sun. They have always been adequately watered. They never did very well. The leaves turned a sort of red and eventually browned out. Could it be the soil in the pots, or do you have any other ideas?
Zonal geraniums are great colorful additions to your area. These geraniums do well in full sun, like yours have, and light, well-drained soil with consistent watering. A good potting soil with additional vermiculite is a good choice. Are your pots outdoors or indoors?
The leaves turning red then brown sounds like a problem with watering - either too much or too little. Plant roots require air and oxygen as well as water to function well. Make sure your pots drain excess water from the drainage holes when you water. Wait until the soil is dry down 2 inches before watering again. That gives the soil a chance to drain and the soil pores to fill with air, while keeping the soil particles moist. This article has additional information on growing zonal geraniums, How to Buy and Care for Geraniums https://extension.oregonstate.edu/news/how-buy-care-geraniums.