Well, good for you getting some knowledge first. And that testing kit is pretty good, but doesn't test hardness...if you can find out what your hardness is from your water company that will be good.
Now then, you need to do daily water changes. Use Seachem Prime to treat your water. It will neutralize the toxins and remove ammonia, for a time...it will of course come back with that many fish, especially the wrong kind for such a tank! It will help a great deal though, and makes it less toxic to the fish.
It's a bit touchy, but if you can find someone willing to take the silver dollars and care for them while in bad shape, you should do so. If not, I would suggest you try to get them into better shape before you get rid of them, which is going to be hard in such a small tank for them. It sounds like they have fin rot, not bites. The smaller one may be a young silver dollar, but it could also be some type of tetra or barb, there are a few with similar shapes, and who knows what color they would be with such poor care. Most of those fish aren't biters, but the silver dollars MIGHT be chewing on each other to run them off and get more space. Clean water will get it done, do 30% changes daily, if your ammonia rises instead of falls do 50% changes daily until it's settled. It's in a mini cycle right now. You want ammonia at zero, nitrites need to be zero as well, and nitrates are tolerable below 20ppm, but at this point with injured and poorly cared for fish, you want them as low as possible. If you can get your hands on some live plants, that will help bring the toxins down faster, especially if you get a bunch of stem plants. It's hard to get them to zero without live plants. Stem plants are easy and require little care and low light, you can also break them in half when long enough and replant the clippings to grow.
Now the other issue is you have a hexagon tank. That's the wrong kind of tank for danios or tetras, and especially for your silver dollars, poor things(that guy sucks, just thought I'd put that out there). Most tetras anyways...this being because they love space to zip around and swim and they require long tanks and larger groups. I would also suggest you get rid of the danio once he's doing better. The only tetra I can think of that would go in there ok is the Cardinal Tetra, they aren't as active and if the tank is at least 1.5-2 feet long it should be ok for a group of six or seven. Most fish like long over tall or funny shaped tanks though, so it'll take some looking to find fish that would be ok with it. Someone else will probably have much better ideas for you.
Now algae eaters...that's certainly an issue. Do you know what kind they are? If they're plecos you MUST find out what kind they are, the only kind that could fit in a small tank like that is Zebra Plecos, Otos, Rubber-lips and a few species that get no larger than four inches. Most species get much larger, and since the tank is a hexagon and not a long tank, if there's any more than 3-4 inches it's gonna be stressful for them. They also need long tanks or they get cramped and risk stunting.
If they're Chinese algae eaters...get rid of them right away. They will actually feed on your other fishes slime coats and eventually cause issues that kill them. Once they start, even with the right food put in for them, they still wont stop. If they are, this might be the cause of damage to the other fish.
So keeping the water clean and treated with a lot of testing to make sure things are settling down right, their fins should heal. You may want a light antibacterial medication in a week or so if things don't start looking better. If they do, you're probably fine.
FILTER! I hope you didn't change it out or wash it. Doing so kills the beneficial bacterial colonies that keep the tank cycled. There's actually very little of them in the substrate, the filter is the key to a healthy tank. Don't wash and change it very often, whenever you DO change your filter cartridge or sponge, be sure you put in a new one with the old for at least a week first so the colonies can move to them and make it home. If you just clean it all out or change the cartridges/sponges, you send the tank into a cycle and it could take several weeks to a few months to fix, during which time your fish will be attacked by the toxins in the water and could die. If they survive a full cycle, their immune systems are usually trashed for life.
I suggest you read around on here, find what you need. Ask specific questions so you get all that info on that one thing and don't get mixed up. =) You will learn! It's so good of you to do research. Bravo. Many are like the person who sold you the tank and don't care to even check things out.
Now then, you need to do daily water changes. Use Seachem Prime to treat your water. It will neutralize the toxins and remove ammonia, for a time...it will of course come back with that many fish, especially the wrong kind for such a tank! It will help a great deal though, and makes it less toxic to the fish.
It's a bit touchy, but if you can find someone willing to take the silver dollars and care for them while in bad shape, you should do so. If not, I would suggest you try to get them into better shape before you get rid of them, which is going to be hard in such a small tank for them. It sounds like they have fin rot, not bites. The smaller one may be a young silver dollar, but it could also be some type of tetra or barb, there are a few with similar shapes, and who knows what color they would be with such poor care. Most of those fish aren't biters, but the silver dollars MIGHT be chewing on each other to run them off and get more space. Clean water will get it done, do 30% changes daily, if your ammonia rises instead of falls do 50% changes daily until it's settled. It's in a mini cycle right now. You want ammonia at zero, nitrites need to be zero as well, and nitrates are tolerable below 20ppm, but at this point with injured and poorly cared for fish, you want them as low as possible. If you can get your hands on some live plants, that will help bring the toxins down faster, especially if you get a bunch of stem plants. It's hard to get them to zero without live plants. Stem plants are easy and require little care and low light, you can also break them in half when long enough and replant the clippings to grow.
Now the other issue is you have a hexagon tank. That's the wrong kind of tank for danios or tetras, and especially for your silver dollars, poor things(that guy sucks, just thought I'd put that out there). Most tetras anyways...this being because they love space to zip around and swim and they require long tanks and larger groups. I would also suggest you get rid of the danio once he's doing better. The only tetra I can think of that would go in there ok is the Cardinal Tetra, they aren't as active and if the tank is at least 1.5-2 feet long it should be ok for a group of six or seven. Most fish like long over tall or funny shaped tanks though, so it'll take some looking to find fish that would be ok with it. Someone else will probably have much better ideas for you.
Now algae eaters...that's certainly an issue. Do you know what kind they are? If they're plecos you MUST find out what kind they are, the only kind that could fit in a small tank like that is Zebra Plecos, Otos, Rubber-lips and a few species that get no larger than four inches. Most species get much larger, and since the tank is a hexagon and not a long tank, if there's any more than 3-4 inches it's gonna be stressful for them. They also need long tanks or they get cramped and risk stunting.
If they're Chinese algae eaters...get rid of them right away. They will actually feed on your other fishes slime coats and eventually cause issues that kill them. Once they start, even with the right food put in for them, they still wont stop. If they are, this might be the cause of damage to the other fish.
So keeping the water clean and treated with a lot of testing to make sure things are settling down right, their fins should heal. You may want a light antibacterial medication in a week or so if things don't start looking better. If they do, you're probably fine.
FILTER! I hope you didn't change it out or wash it. Doing so kills the beneficial bacterial colonies that keep the tank cycled. There's actually very little of them in the substrate, the filter is the key to a healthy tank. Don't wash and change it very often, whenever you DO change your filter cartridge or sponge, be sure you put in a new one with the old for at least a week first so the colonies can move to them and make it home. If you just clean it all out or change the cartridges/sponges, you send the tank into a cycle and it could take several weeks to a few months to fix, during which time your fish will be attacked by the toxins in the water and could die. If they survive a full cycle, their immune systems are usually trashed for life.
I suggest you read around on here, find what you need. Ask specific questions so you get all that info on that one thing and don't get mixed up. =) You will learn! It's so good of you to do research. Bravo. Many are like the person who sold you the tank and don't care to even check things out.
