Actually, in my experience, the most common color for spider mites is a reddish brown, though I've seen beige before. If it makes webs like a spider mite, and it sucks plant sap like a spider mite, it's probably a spider mite.

I went through this myself a while back with Calathea ornata, which is documented at my blog. I was not as diligent about trying to remove the mites as I could have been, but even so, a lot of time was wasted on them, and in the end nothing actually improved. Mites can be very persistent on Calathea and related genera (Maranta, Ctenanthe, Stromanthe).

You could try soapy water, though I think it's probably not likely to help that much in this case. Neem oil may work better, and placing the plant outside in a protected spot might also help, but if it were my plant, I'd be likely to call it a lost cause. Then again, it wouldn't be my plant, because after my Calathea ornata experience, I swore off Calatheas forever, so my judgment about what is or isn't a lost cause might be a little glitchy in this case. Someone else might be more encouraging.

Calatheas are spider mite magnets.
Fortunately they are rhizomatous so can stand being cut back to the ground if you have to. They will grow back.
I'd use a dedicated miticide like Kelthane. It smost commonly sold here at Feed Stores but you can get it online. Take your plant outside and pretty much douse it on all leaf and stem surfaces. If you can leave it outside for a few weeks, I would, and I would re-spray it every 3-5 days for 3-4 weeks. Mites are hard to kill, you have to get the new hatchlings as they hatch, because most things don;t kill the eggs, and mites are actually born pregnant, so you have to get them before they can lay new eggs.

After a month of miticide I would still spray every 7-10 days with Neem or soap. A friend of mine started using dog flea soap (with Pyrethrin) and said it works better than plain old soap.

I have several C. ornatas (I have to keep dividing my main plant, which is in-ground and is 6 ft tall) and have fought mites on it and other differnet calatheas on and off for years. SOme plants just attract mites and Calathea is one.

Thanks for the responses. After a thorough shower last time, the same pests have appeared. This time I took a picture before showering them off. They're a little hard to make out - they are the white 1mm dots on the webs. They were crawling up and down the webs.

{{gwi:88704}}

Are these spider mites?

I believe they are, yes.

The plant is going down-hill fast. It's sitting next to a thriving golden pothos - any danger of spreading?

I'll probably just dump the calathea. Is it safe to keep the plastic potter it is in?

The mites may spread to the pothos, though the main danger of that is not to the pothos, but to the other plants in your home. Pothos can get mite infestations, though it's uncommon for them to get mites so badly that their appearance is hugely affected. They're just not that good of a host for mites. However, as long as there are some mites there, the pothos could act as a reservoir of mites and cause a reinfestation later. This isn't a big enough threat that it would cause me to throw away a thriving plant, but it's something to bear in mind. You might consider preventatively treating the pothos for mites, at least.

As far as I know, yes, it's safe to keep the pot. You'll probably want to wash it off before re-using, just because it may be dirty, but I don't think you have to do this to get rid of mites necessarily. I don't think they can live long without eating, so any mites that are still on or in the pot will be dead shortly, and the pot should be safe to reuse.