10 gallon fish tank with filthy water HELP!!!?

The key here is to change things gradually and stress the fish as little as possible. Fish can go into shock if there's sudden changes in water parameters, including from very dirty to very clean water, and that can kill them. It is very easy to lose all the fish when you try a sudden huge cleaning. So I'll detail how to do each step in the process safely.

You should start with partial water changes of 10% to 15%, during which time you will also gravel vacuum. You can leave the fish in the tank during partial water changes. Do that each day until the detritus has all been sucked up by the gravel vacuum, which may take a few days.

Also, if you already have a filter don't throw it or the media within it out. That's where the beneficial bacteria that keep the tank cycled and stable live, and if you throw them all out there will be dangerous spikes in nitrogenous wastes. Instead of throwing them out you can clean 1/3 of the filter media at a time. To do that, use dechlorinated water or old tank water in a ziplock bag and clean the media in there. Then put the cleaned filter media back. If you want to switch filters, it would be best to run the new filter on the tank in addition to the old filter for a month or so. That way you can basically clone the cycle so that the new filter is eventually full of enough bacteria to keep the tank stable. You will want to clean out the intake tube of the old filter, though, which often becomes clogged with detritus in dirty tanks, keeping the filter from working well.

Assuming there is lots of algae on the tank walls, you might want to go ahead and get an algae scraper with a metal razor. That will remove lots of algae from the walls of the tank very easily. Seachem makes a nice three in one algae scraper that includes a razor, you can get the short version since your tank is small. Now that I've found out about metal algae scrapers I don't see ever going back to another kind. It should make cleaning the tank a lot easier. Do be careful, of course, as it is sharp.

As for the decor, plastic plants, rocks, etc. can be cleaned with a 20 parts water to 1 part bleach solution outside of the tank. Soak them for about 10 minutes in that solution, then rinse them thoroughly until you can no longer smell any bleach. Then you can soak them in a container with heavily dechlorinated water - 5 times the recommended amount. Rinse them thoroughly again the next day and the decor should be fine to go back into the tank. Make sure never to use soap with any kind of aquarium decor or other equipment, as if you use soap it will never again be safe for fish.

Substrate is nearly impossible to clean, so that is likely going to just have to be changed out. There is, again, some beneficial bacteria in the substrate, so only change 1/3 of it out a time. I would wait to change it out until you've sucked up most of the gunk in the tank, though, so the new stuff doesn't get too dirty right away.

You may have some hard water deposits on the lid and light. That should be cleaned outside of the tank with vinegar. The vinegar will soften the deposits, then you can scrub them off, rinse the lid, and wipe everything down before putting the lid back on it the tank. Allow the light to dry off thoroughly before plugging it back in. 

Keep an eye on the missing eye for any signs of infection - bacterial or fungal. Keeping the water clean will help from now on. If you've been having trouble doing water changes because of carrying buckets back and forth, you might want to invest in a python water changing system that hooks directly to your faucet. That should make water changes easier so you will be more likely to stick to the habit of changing the water each week. 30-40% water changes each week should maintain things after you've gotten everything back in order. You should also check about whether the fish you have need larger groups or not, and plan on addressing that once everything is stable again.

Akeath thanks so much!! I'm going to be doing a 10-15% water change starting today, for everyday until all the detritus has been sucked up. I do have a filter so I will be cleaning it as you specified with dechlorinated water. Thankfully the tank walls don't have too much algae, but I'm definitely going to be purchasing a metal algae scrapper. As for the lid it actually has been cleaned so that's already looking new and fresh. I don't currently have substrate, but I may look towards investing in some once everything's in check. I will be thoroughly cleaning the plants next weekend, and am going to invest in some new tank mates once I'm sure that I've got a mini paradise in my tank. As for my fish pirate I will be closely monitoring the eye!! 

You need to set up a temporary spare tank for the surviving fish. Fill it with water and let it stand for three weeks then transfer the fish. It won't need any gravel etc but a air supply would be beneficial. 

On to the old tank. Dump all the old contents as bacteria will hide in everything. Then use sea salt on a damp cloth to clean the interior. Salt will not scratch glass and it's an very effective bactericide. Rinse well of course. Maybe a hose outside. Then restock the tank with gravel and run the filter. You could consider using false, plastic weeds and rocks as natural weed is a pain and can introduce pests. Leave the tank to settle for a fortnight and pop your heroic fish in.

I suggest you start over.  And don't neglect your tank this time.

And the circumstances of the death of your CAPTIVE ANIMALS is your NEGLECT.