Houseplants keep getting infections

Question

Over the past year we've tried to grow several small houseplants in our apartment, but every one of them has succumbed to an infection of some sort. For what it's worth, we keep our house spotless, so it's not like there's (visible) mold growing anywhere that could be a vector. Here are some examples of our casualties:

• Spruce bonsai: spruce mites
• Aloe: white mold (unsure what kind)
• Amaryllis: bulb rot (red, not sure exactly what kind), and Southern Blight
• Heart-leaf philodendron: Southern Blight

All plants were watered exactly as instructed, most kept in draining pots. They were also either in a location with plenty of sunlight, or were supplemented with a grow-lamp like this one. I really want some kind of plants in here, but I don't want to spend the time and effort if they're just going to get infected again. So my question is two-fold:

1. Is there possibly a single reason why all these infections are happening (and what can I do about it, if anything)?
2. Are there any houseplants that would be resistant to these types of infections which would be safer to try? Or growing/care techniques to fight infection?

Edit based on comments:

None of these plants were ever outdoors (aside from transporting them from their origin store or house). Aloe and spruce were watered 1-2 times per week based on soil dryness. Philodendron was watered 2-3 times per week based on soil dryness. Plants were watered until it began to flush out of the drain. Amaryllis was kept in a large glass vase with pebbles and water filled to cover the bulb, water was changed once per week and the pebbles were washed, damaged parts of the bulb removed when the red rot started showing, Southern Blight-like mold/symptoms started showing above the water line towards the end. All others were kept in their original potting soil. I didn't have any of the infections lab-tested, but the mites were easy to identify and the Southern Blight I'm 90% sure about based on appearance/symptoms and that it's endemic to my area.

Answer 1

In regard to the Amaryllis, you've said you kept the water topped up to cover the bulb - that's why it rotted, the water should be below the base of the bulb only, where the roots are. If the actual bulb is sitting in water, it rots.

The spruce bonsai is intended to be an outdoor bonsai, except when the weather is very cold in winter; if it had a problem with mites, it must have come into the house with them, because it couldn't have become infested inside the house.

If both the Aloe and the Philodendron succumbed to a fungal infection, that would suggest your watering regime needs improvement. Aloe must have some sunlight, so a sunny windowsill would have been the best spot for that - watering in winter is minimal, only once every 1-2 months, but from spring to autumn, should be watered as any other houseplant. The way to water is to touch the top of the potting soil, pick up the pot - if the top of the soil feels dry to the touch, and the pot reasonably light, water thoroughly, then empty any outer tray or pot after 30 minutes so the plant is not left sitting in water.

Unless your apartment is very dark, growlights shouldn't really be necessary. Philodendron do not appreciate direct sunlight, they prefer light shade or moderate brightness. If it was one of the larger varieties of Philodendron, and you had it for a year, it likely also needed potting up into something larger in that time, unless it was in something large when you bought it. Most houseplants prefer bright daylight with no direct sun - some tolerate quite moderate or low light levels. The majority need watering in the way described above. Note that Southern Blight is an outdoor infection, a problem in gardens, but there are many fungal infections to which plants can succumb in damp or wet conditions indoors.