Should we move the fish over and scrub tank down, or just change the filter?

Usually it's not the tank itself that is the problem, but the water quality. Unless, of course, the tank is too small for the stocking you have, which could be a big problem. There are three different species sold under the Glo-fish label, and all of them actually have a 20 gallon (80 litre) minimum tank size, despite the fad to put them in small tanks that the Glo-fish is making money off of. So if your tank is smaller than that, by all means get another one and transfer the filter with media over to run side by side with the new filter for the first month or so. But if it is adequately sized, then you should be doing daily partial water changes, complete with a thorough gravel vacuuming, every day to get the water quality and detritus under control.

The likeliest reason your fish are dying is because your filter isn't mature yet, and your aquarium is going through what is called the cycling process. In a mature filter, there is a bunch of beneficial bacteria in the filter media that take the toxic Ammonia fish produce and break it down to Nitrite, and then to Nitrate. Each step makes the waste a lot less toxic. But in new tanks set up for less than a month, there isn't a big enough colony of bacteria to take care of the fish waste. In the mean time, waste stays in it's most toxic form and poisons the fish, causing their deaths. If you put a bunch of fish in before the first month is up, it is very likely some will die. You need to do daily water changes and stock very lightly if you put fish in that first month.

It's generally a bad idea to take down a tank and clean everything. It gets rid of all the beneficial bacteria without really helping much else. And if you use soap or other chemicals, the tank won't ever be safe for fish again. Incidentally, the vast majority of the beneficial bacteria live in the filter, so just changing the filter can also be very bad for water quality. Usually, it's best to clean the filter media in a container of tank water outside of the tank, then put the filter media back in. And if you get another filter, run the old one alongside it for a month, so that the new filter will be mature by the time you get rid of the old one, or you'll have to go through the whole bad water quality thing again.

Here are directions on partial water changes and tank maintenance, to try and keep the water quality as high as possible: http://www.aquahobby.com/articles/e_waterchange.ph...

Edited to add: 8 Glofish and a snail in a 10 gallon would be overstocked, and it's no wonder your fish didn't handle that well, especially if the tank was new. You need at least a 20 gallon, and a more powerful filter on that 20 gallon. You can run the old filter along in the new tank for whatever bacteria have already gotten in there. Add the current fish into the new 20 gallon, with an acclimation in a bag just like you did when you got the fish. Do daily partial water changes for the first month. Then gradually add in 2-3 more of the specific Glofish species you got every few days till you reach 8, which is the minimum schooling number for all 3 of the Glofish species, since they can all be fin nippers with harsh pecking orders within their school.

They're the smaller Glo fish, less than an inch each and they're in a 10 gallon tank. Plenty of room for 8 but we lost the first three very quickly, so there were only 5 for a few weeks and we just lost 2 more last night.

We have test strips, it's acidic. All else is fine.

We were doing partial replacements every couple of days for a long time but it didn't help. It hasn't been as frequent lately. Suddenly it's getting worse (as evidenced by the 2 additional dead fish).

The filter is not good, it needs to be replaced. There is stuff all over the plants and gravel, so I think it would be good to clean them, but I don't want to hurt anything...

How big are your fish and how big is the tank?

Generally speaking, the more space the better.

Second, test your tank's water, if you don't have a testing kit take a sample of your water into the nearest pet shop and they will usually test it for free.

Check online to find the best balances for your specific type of fish.

Generally speaking it is not a good idea to move them to a completely fresh un-cycled tank, especially if you believe that they are sick.

Without knowing the size of your fish, their tank, and the reading for your water it will be very hard for anyone to help you.

I strongly advise you test your water at home, or take it in to get it tested before you do anything as drastic as re-booting their tank.

Please also look into cycling your tank if you do decide to start over and make sure it is cycled properly.

What is their behavior before they die? What temperature is their water? Have you tested your water at all? If you have, it would be helpful to know what your parameters are in ppm. The snail may have died because the tank is acidic. Snails need basic/alkaline water. What do you mean when you say there is yuck in the water? How often do you clean your tank and how do yoh clean it?

As is, the amount of information you gave isn't enough to troubleshoot the issue.

Seems like something is wrong with your water, I would recommend you to do a 60% water change and add a bottle call "stress coat" to help. And go ahead and replace your filter media. and always remember different species requires different water conditions. temps, ph, soft etc etc,,, so ask your fish guy which fish are capable with which. GOOD Luck !