Plantkiller.....(I don't believe that though)
I'll suggest something....not necessarily though what might help all of the plants.

Common houseplant pests do prefer some plants more than others...some plants are notorious for drawing certain pests.
Some pests cannot be harmed by simply spraying soap and water. Let's do away with the term soap if we mean we are using "detergent". Soap is what is meant by any advice in that regard. Detergent may be too harsh....even toxic.

The scale insects have a body armour that soap will not affect. For this reason when using a 40 to 1 solution soap and water, the additional adding of 8 parts rubbing alcohol is advised. This also applies to the pest "mealybugs".

About spider mites. You have evidently identified the pest as such....and the first thing you should have done when first noticing such pest was to isolate any and all plants away from each other. Spider mites, as you are aware of now, spread like wildfire.

Any pest that is on the plant can have its beginnings by being either air-borne--much like a fungus; or be soil-borne. The adults have kiddies....eggs...which they lay on the plant in secretive places--usually underleaf or in the crotches...and if like the scale insect, such soap and water runs off of them like the proverbial duck.
There they remain until the eggs hatch into larvae...and in a few days become adults....to start the whole process over again. This is why you must isolate them.

The treatment done every few days was probably OK....usually the recommendation is to do it 3 times over a span of 10 days. i.e. today, in five days, and again in five days. If the pest is sitll noticed, another treatment is done. Then vigil is kept to keep them away.

Whether you can safely dunk a plant's leaves into the soapy solution rather than spraying.....that's an unknown method to me.....but, any soap and water solution given any plant, must be followed by a thorough rinse.
Soap is an astringent...it dries the surface much like if we were to leave soap on our skin. The soil the plants are in, must be considered as a possible homesite for the eggs and larvae. So the soil should be treated likewise. This may prove difficult because we don't wish to overwater the plant. Generally such invasion would be contained in the top inch or two of soil. This might be examined, possibly removed and replaced with fresh if considered a way to control.

You can always try the leaching method. Dunk the plant wholly in water...pot and all. Leave for the time the bubbles take to stop. This ensures all cavities of the soil has water. Bugs are air breathers....they must come up to breathe. As they do, you dispose of them.

Treat this as a thorough watering and allow the plant to dry down as is normal practice. This treatment though, should not be done on a regular basis. Once or twice a season is sufficient. The plant must drain well.

The usual damage that spider mites do is that the leaves will yellow and die or fall off. The leaves too may become mottled with brown or yellow spots and the undersides of leaves have the tell-talke webbing which might not react to the soap and water.
Aside from soap and water, some chemical applications are used. For spider mites, lime sulfur (much the same as you use in spring when applying dormant oil/lime sulfur to deciduous trees, shrubs and roses).
Dusting sulfur or the dormant oil itself is often used.
Regular misting of the plant is also a deterrent to the return of spider mites.

With so many plants affected, I can guess your anxiety.
Let's hope we can get the problem under control.

Brown tips and fronds are most likely because of humidity or temperature problems; peace lilies (Spathiphyllum) and spider plants (Chlorophytum) in particular will do that if they're too wet.

None of the plants you list are especially prone to spider mite problems; mites tend to like English ivy (Hedera helix), Scheffleras (Schefflera actinophylla, S. arboricola), crotons (Codiaeum variegatum), palms (especially Chamaedorea elegans), Hibiscus, false aralia (Dizygotheca elegantissima) and related plants. So this shouldn't be an impossible situation.

You could spray with soapy water more often than just once a week. It'd be nice if you can use a hose or detachable shower spray to wet down the foliage, too, just because anything you can do to knock the mites physically away from the plant is helpful, but that may not be practical in this situation. Dunking plants in soapy warm or room-temperature water may help somewhat too. Whichever method you use, you should be careful not to accidentally overwater the plants as you're treating them: you may kill the plant with water while trying to save it from mites.

I don't know what the orange residue from the spider plants might be; I don't think it's necessarily related to the mites.

Different treatments for different plants? Well, maybe if soapy water doesn't work after a few weeks, you could move on to more intense things (neem oil, or other horticultural soaps or oils) but at least for the stuff you list, that should be okay.

Mites can still be around even if you don't see webbing and stuff, but I don't know any better ways to try to find them than looking for webs and tapping them on to white paper.

I wouldn't worry overly much about mites anywhere other than the plants; they can't actually crawl very far on their own power. They can float around on air currents for a while, if they're brushed into the air, so getting the air filters changed for the office might help a little bit, but I don't think it'd make a lot of difference. Vacuuming is probably more helpful than anything else you can do: you don't necessarily want to vacuum the plants themselves, but a little extra vacuuming around the plants isn't going to hurt anything. Humid air, cooler air, and moving air will all set back their reproduction a little bit.

One thing you need to bear in mind is that this time of year, spider mites are problems for a lot of people; they like the hot, dry air of central heating. If you're not in a situation where you can dictate the temperature on the thermostat, or introduce a humidifier, the better approach is probably to stick to plants that are less likely to have problems with mites.

The only thing I found truly effective for spider mites is to hose off the plant in the sink to remove as many mites as possible. When dry I use Ortho's Systemic spray. The entire plant becomes toxic and bye bye spider mites, mealy bugs and other no-good-nicks. Neem oil may work but by the time it worked on my tomatoes half the plants were dead. I couldn't use a systemic on food plants. Humidity doesn't help as my greenhouse and sun room are in the high range and the spiders thrive.

If you can't seem to get a handle on the mite problems (although I hope you can) Put the plants outside in the spring, maybe a bright shaded or semi area when the temps warm up, tilt the plants on their sides and turn them as you hose, hose and re-hose them down with plain old water.
The outdoor humidity after a while should help get rid of any stragglers.That's what I did with my Calamondin (dwarf orange tree) and it now been spidermite free and has been since last spring.

Billy Rae

Plant killer, you do need to do a bit of research about individual plants before using a specific treatment. For example, oils and insecticidal soaps may damage jade and even some cacti. Ferns are notoriously sensitive to chemicals.

I have. What I am using is a very small amount of gentle dish soap w/t water. The main problem I seem to be having is that I don't really want to use chemicals but I'm not sure if the little buggars are gone... I don't really want to use anything harsher on my plants in case it damages them but I'm running out of options. The ferns are in pretty rough shape, the jade LOOKS healthy but its dropping an abnormal amount of leaves, the rest of the plants look fine except for some brown tips and a few brown edges.

Should I 'wait and see' a little longer or just try dunking a couple of the hardier ones to see how it turns out? lol.

I wish I had read this thread before panicking and throwing out a croton and a pony tail; the pony tail in particular was infested and I did not see this slowly spreading until it was too late. I noticed some webbing on the croton, nothing too serious, brushed it off, but the plant next to it was the pony tail and it must have spread because it was really bad. I have never had a serious problem with insect infestation except fungus gnats in the summer months, and I just immediately dumped both plants; I'm hoping it hasn't spread. I am genuinely afraid to look further and discover any more bad news, since I have 80 plus houseplants in one large room.

Since reading these posts I will force myself to look for more signs and follow along to see what advice is being given - Rhizo, thanks for mentioning that individual plants need individual treatment, I had no idea, although I suppose it should be obvious. Good luck, plantkiller!

Eileen, getting rid of spider mites on a croton is a real challenge. I usually throw them out right away to keep from infesting nearby plants, so you did the right thing!

Glad to hear I did the right thing watergal, it makes me feel a little better. Right now I am losing it because one of my prayer plants is swarming with mealy bugs. Insects are the worst!

If the plant can handle it try putting it in a clear bag like from a dry cleaner this will increase the humidity. I leave some opening for circulation. Prayer plants love this, be careful not to overdo it.

Here is a link that might be useful: How to Identify Insects On Houseplants

uh oh, what are fungus gnats? There are a lot of little fruit fly lookin things down there... I thought it was the humidity... *holds breath for reassurance*

You guys are great by the way. I really appriciate all the help. You've saved my butt a few times already. lol.

ok, I'm gonna go for it... I LOVE my plants but if they die they die... I've got a lot of great advice to work with now and actually I just read another thread that really helped to... I think

-They all have evil super mites
-My Peace lillies are overwatered
-Perhaps fertalizer burn on some of them... from what i just read it sounds likely....

My treatment plan for the smaller pots is:
-Dunk the pots in water in case of spider mites lurking in soil
-Run some water through in case of fertalizer buildup
-Dunk the tops (the actual plants) in soapy water, then rinse. (I dunked the baby spider plants in soapy water last week because they were too hard to spray and they are doing better than any other part of any other plant in the room. lol)
-Spray down the giant plants and icolate them, I think they have the best chance, even the ones that showed webbing for a while are doing MUCH better than the little plants are. They all look pretty good until you scrunch right now next to them and get all clinical squinty eyed. ;)

So, do we think this is going to work? lol...

-Plantkiller

oh, any Jade plant experts out there by the way? Mine has recently started dropping leaves like crazy but I dont know ANYTHING about them. This one is my moms but shes in mexico for 5 weeks so i'm looking after it.. badly I guess. lol...
It started with the mites, some kind of fungus growing on the soil on one side but thats gone now... now the leaves are curling and dropping, some look crystalized???

Tobacco juice. Gets rid of mites and fungus gnats better than anything I've ever used.