Why do my plant leaves keep turning yellow and what can I do to prevent it from happening again?

I totally get how frustrating it can be to see your plants' leaves turning yellow, especially when you're just starting out with indoor gardening. I've been there too, and it took me a while to figure out what was going on with my own plants. One thing that might be happening is that your plants are getting too much water, which can cause the roots to rot and lead to yellowing leaves. So, even if you're adjusting your watering schedule, it's possible that the soil is still too wet.

I'd recommend checking the moisture level of your soil by sticking your finger into it up to the first knuckle - if it feels wet, it's probably too much water. You can also try letting the top inch of soil dry out between waterings to see if that helps. Another thing to consider is the type of plants you're using - some plants are more prone to yellowing leaves than others, so it might be worth looking into the specific needs of your plants to see if there's something you can adjust.

As for tests you can run to determine the cause of the yellowing leaves, you can try checking the pH level of your soil using a DIY kit or by sending a sample to a lab for analysis. This can help you figure out if your soil is too acidic or alkaline, which can affect how well your plants absorb nutrients. You can also try fertilizing with a balanced fertilizer to see if that helps - just be sure not to overdo it, as too much fertilizer can be just as bad as not enough.

Overall, I think the key to keeping your plants healthy is to pay attention to their individual needs and make adjustments as needed. Don't be too hard on yourself if you're not getting it right away - it takes time and practice to become a good indoor gardener. If you're still having trouble, feel free to share more about your plants and I'd be happy to try and help you troubleshoot - good luck, and I hope your plants start thriving soon!