The leaves of one of my large plants are yellowing. I’ve not been over watering it but I do use water from my fish tank when I do water it. Could it be getting over fertilized?
Is it well enough drained? Yellowing can be caused by poor drainage. Also, one reason to do water changes in your fish tank is to prevent buildup of salts. If this plant is very salt sensitive, using fishwater could be the problem.
Take the plant outside and run clean water through it’s soil for several minutes. This is called flushing, and it will remove any excess salts that have built up.
Perhaps there is too much ammonia in the fish water.