Hi, Hello And Help!!!

The first thing to say is that the advice to water changes was good. You need to be doing them daily at the moment.

A quick lesson in the nitrogen cycle - don't worry, it's not too complicated 
Fish make ammonia - it's in their waste and they breathe it out. But ammonia is toxic, it burns the fish's skin and gills making it hard for them to breathe. In a tank which has a cycled filter, there is a colony of bacteria in the filter which eat the ammonia and turn it into nitrite. But nitrite is also toxic - it binds to the fish's blood making it hard for the blood to absorb oxygen. In a cycled filter, there is a second colony of bacteria which eats nitrite and turns it into nitrate. This is only toxic at high levels.
Cycling is the term used for growing these bacteria and it takes several weeks, even months. Despite what the shop would have us believe, very few of the cycling products, such as the API one you used, do it instantly.
You are now doing what is called a fish-in cycle and it will need some work on your part to keep the fish alive until the filter cycles. This is something that very few shops will tell you.

The way to do a fish-in cycle is to do as many water changes of a big a volume as necessary to stop both ammonia and nitrite from ever getting higher than 0.25. If either are 0.25 when you measure, you need to do a water change immediately as it will go above that by the time you test again. To be honest, the lady at the aquatics centre is a bit cautious saying 25% every other day. You need to be guided by the test results; if necessary you can do 90% every day. Water changes are stressful for fish, but being poisoned is even more stressful.
The Pure Aqua may help or it might not. From now on, test the water every day, or twice a day if you can manage it, and do a water change every time you see the reading for ammonia or nitrite approaching 0.25. With just the danios in there they shouldn't go up too fast.

Here is a 'how to' thread on fish-in cycling
http://www.thinkfish.co.uk/forum/index.php/topic,17.0.html



As for the sickness, that is probably down to the poor water conditions. Having ammonia and/or nitrite in the water makes the fish stressed and more susceptible to infection. Keep on treating the fish. If the med has to be added daily, do a water change then add it. If the med is not dosed every day, on non-dose days add enough med to replace what was in the water you just took out eg if you remove 20 litres, add enough med to treat 20 litres.
Once you have successfully treated the fish, put some new carbon back in the filter to remove the left over med, then after a few days take it out and throw it away together with all the med stuck to it. Then, if it was my tank, I'd fill the carbon space with more sponge or ceramics as you don't actually need to run carbon full time.







Oh, and don't replace the sponges and ceramics like the manual probably says. You will have spent several weeks growing your bacteria, the last thing you want is to throw them away. Sponges and ceramic will last for years.

At 0.4, you need to do a water change. At least 50% (more is better) to get it down below 0.25. Big water changes are safe so long as you get the new water to around the same temperature as the water still in there. Feeling it with your hand to compare will get it close enough.
You will find yourself having to do daily water changes for a while, then it'll be a couple of days before either/both ammonia and nitrite get high enough to need a water change. Slowly, you'll be able to go longer and longer between water changes, then one day you'll realise it's been a week since you had to do the last one, and that both have been at zero all week. That's when the filter will be cycled, and you can do weekly maintenance water changes.
As I said in the link, once you reach the point of zeros for a week, don't go and get a lot more fish at once. There will only be enough bacteria to cope with the ammonia from the fish you have. Adding too many more at one go will create so much ammonia the bacteria won't be able to cope. Slow and steady is the way to do it.

Have you found the community creator yet? It's a tool that tells you if a fish you like is suitable, and whether all the fish you want will fit. It's accessed through the fish profiles (see menu bar at top). Click on any fish and scroll down to the bottom of the profile.



Dose the cotton mouth med after a water change. I would hold off the whitespot treatment yet as it isn't usually a good idea to add more than one med at a time. Do the fish look like they've been sprinkled with salt or is it just the flashing? Because ammonia in the water irritates the skin and can make the fish flash to relieve it, so unless there are salt-like spots, I wouldn't use that med yet, concentrate on the other.

Is the Nutrafin test kit one of those that only "less than" something as its lowest colour? If it is, then aim to keep both ammonia and nitrite at the lowest one.

The salt will help with the nitrite, and can also help with whitespot in conjunction with a raised temperature (30^oC) But if what you also have is columnaris, raising the temp is not a good idea.

The white patches - are they grain of salt size or bigger?
If bigger, carry on with the first med.
If they are 'grains of salt' you need to remove the first med before treating. Do a big water change then put carbon in the filter for 24 hours. The water change will remove a lot of the first med and the carbon will get the rest. Then add the whitespot med. You need to follow the instructions to the letter. This explains about whitespot and its lifecycle http://www.thinkfish.co.uk/health/whitespot.html The parasite can only be killed in the free swimming stage and since there will be parasites in all the stages in a tank, there must be some medication in the tank when every last one gets to the stage where it can be killed. Since it is probably not a food idea to increase the temp in your case, I would carry on the treatment a bit longer than it says.
If you find ammonia/nitrite and need to do a water change, don't forget to replace the amount of med you take out after you've finished.


The filter bacteria live in the biofilm that grows on every surface in the tank. They just grow mostly in the filter as there's lots of water flowing through bringing oxygen and food, and the media is designed to have a huge surface area so plenty of room for the bacteria.
White sponges do go a brownish colour, but it is impossible to say by looking at it whether the bacteria are growing or not. The fact that you have nitrite means you must have some algae eaters. Increasing nitrate would show that you have nitrite eaters but with all the water changes you are doing, coupled with the fact that it is difficult to see small changes with our nitrate testers means that isn't a reliable way to tell. The best way will be when you find the nitrite level is not going up as fast.
The brown gooey stuff building up on the sponge is fish poo, uneaten food and dead bits of plant, if you have any. It should be washed off by gently squeezing the sponge in water that you take out of the tank during a water change.