Why is Grapefruit Inside Dry When Ripe?
Plant is watered and fertilized regularly; this is second harvest.
Certified GKH Gardening Expert
Ultimately, this happens from unavailability of phosphorus.
This can be due to a low soil pH, too much nitrogen, or a true lack of phosphorus in the soil.
This article will offer more information: https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-fruit-thick-rind.htm
Here are some articles to help you test your soil: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
This article will help you to amend your soil: https://www.gardeningknowhow.com/special/organic/the-importance-of-soil-for-an-organic-garden.htm