Looks like the soil is too wet. You need a fast draining potting mix. When you have that it becomes easy to regularly flush out any mineral salt build up and still not have the soil too soggy. When you water sparingly all the water is absorbed or evaporated and the mineral content accumulates in the soil.

@tropicbreezent But I haven't repotted it. Do you mean it was already inthe wrong soil from beginning? Could it be underwatering? I really think I'm a type of person that is prone to underwatering and not overwatering.

Thanks, Photo Synthesis, I will water it more. I didn't flush the soil. So care is similar to the phalaenopsis? I hope it won't die on me as it is the second anthurium and it's exaclty the same problem.

Yes, I even add orchid bark to the fast draining soil, half and half, because Anthuriums are also epiphytes and grow in the same habitats that orchids do.

it needs to be warmer then 68F, it prefers to be above 75F at all times and 75F-85F is the best for it. then you can water it much more often. and it would do better with some warming late-early partial sun, especially in winter.

when they get a chill they throw these huge spots on leaves. Damp and cool does it, usually in winter. It leeds to root rot and those huge spots like you got.

65f is winter for it and 68F is deep fall ;) .

but i see you are in 9b-10b, so you can't be That cold.

Lift it off the floor (it's cooler there) at least and put it into better light. the soil should not be drying up more then half-way at any rate and it should be light enough for you to water once a week. if your soil takes 2 weeks to dry - that's too wet for 68F for sure and you need to lighten the mix as recommended above.

it'll pass once the temps rise and it grows new roots. It looks to be a strong plant, so it should survive this. smaller ones might not though.