Saltwater would work yes. If you can add any essential oils to the water that would be great. Personally, I use resins and sage to cleanse because I really like the heavy-duty shit, but hell you could even go to the store and get yourself a bell for $2 and use that. Though with the magick you’ve been doing without protection you’re probably gonna need to do full banishing rituals and cleansings for a bit.
Regarding the invitation thing- you invited in demons temporarily for them to leave when your ritual is done. But, it seems you have gotten parasites who you did not mean to bring in. Parasites are not the ones we go seeking (well, some do rarely) but that doesn’t mean that just because you used a sigil and their enn you can’t invite anything else. Yes, the chances of drawing the attention of the actual force are very high BUT whenever you do any magickal act there is an effect seen in the other planes by everything around. Anything can enter at that point if it is strong enough. That is why we layer our protections a ton.
Well, it is possible it could be Lilith but (I’m assuming you’re in the northern hemisphere) spiders are very common this time of year and your brain could be making the mental link because of your research. Your dreams could be just about anything.
All in all, no. Cleanse the room a lot for a while. Research just about every protection method there is an use it. I love witches bottles, sachets, evil eyes, bells on the doors, sigils on the wall (usually infused with moon water because I’m in a house that likes new age spirituality shit sadly), I throw salt (black salt is preferable) in the corners, doorways, windows, and near mirrors. I also absolutely adore crystals. All of these things are easily found to research (and buy lmao) on Google. When it’s time to invoke/evoke again cast your circle and all. Cleanse your space before the ritual for at least the first few times. Give it a little while, I waited months to contact anything and in those months I set up a fuck ton of wards.
And honestly, it may not even be necessary to have a full evocation of Asmodeus to get your answer. Granted I do pathworking with him but usually, when I want an answer I’ll just ask aloud before bed and sometimes I get my answer in my dreams, but if that does not work do the evocation after you’ve set up I’d say at least the very very least 10 of those wards.
This is also very worth reading. How to detect imposter spirits and other time wasting things