What could the yellowing be?
I bought this philodendron from Lowes about a month ago. It is actually two in one pot growing together. It is still in quarantine from my other plants, currently in a south window that only gets diffuse light (my other philodendron is in the other window exactly like this in the adjacent room, the same diffuse lighting, and it is very happy). My question is, does this look like early root rot? These yellowish spots have been slowly showing up, but only on the new growth. The up close pictures of leaves are of the newest growth, the two newest leaves on each plant. The small leaf that looks like a bite was taken out of it, I just noticed it looks a little yellow this morning. The rest of the leaves look fine to me. I have checked the back of the leaves and I don't see pests. I have moved around the topsoil and I don't see pests. I really dislike taking plants out of their pots so I guess I need the push to do it. I thought if this was root rot, the yellowing would not only be on newer leaves. The only other thing I can think of is maybe it doesn't like the lighting in this window, but I thought that would also affect all leaves.
I have been watering once the top half of the soil appears dry when I stick a chopstick all the way down the pot. The soil looks like normal potting soil to me but it drains a lot faster. When watering, my goal has been to water thoroughly so I would water until the water comes out the bottom, which is really quick actually, then water a second or two more so I can get the entire top of the soil covered, then hold it over the sink, then put it on a drip tray for a little while before putting it back on it's decorative pot.