New Tank- Fish Poblems

Question
Hi Karen!
I am making a second attempt of a 30 gallon planted aquarium.    I had one for about one year about 2 years ago but due to moving alot I am just now starting my second attempt. The tank is just over three week old.  The plants are doing well.  I have not added many fish.  To start, a week after setting it up I added twon Siamese flying foxes for algae control.  Water conditions seemed optimal (normal pH, obviously low nitrites/ates, the water was a bit hard).  However, after just 4 days the two fish died.  I never saw them getting stressed or having problems.  They were eating up my algae and having a good time.  So I waited a week, checked the conditions again and got two more.  After only two days one of them died- no warning signs at all.  I don't remember it being this hard to keep my fish alive last time.  I'm not sure what to do.  I don't want to not be able to add fish.  Help!

p.s.  possible clues:  using Flourish Excel for carbon dosing? small water parasites seen in water?

Answer
Hi John,
Did you check your ammonia levels? Sometimes they will spike even though a tank has been set up for a few weeks. Usually it will take a tank from 3-6 weeks to completely cycle and then when you add fish it will still have to adjust to the new bio load. It could be that since you added fish only a week after setting up your tank that the ammonia did get  high at some point and the fish were sensitive to the rise. Ammonia in the slightest is hard on fish unless you really keep a close eye on it and immediately do a large water change anytime it starts to rise to dangerous levels. To be safe for your fish ammonia and nitrites should be at 0. Until they get there be sure to keep an eye on both and do a water change as soon as either get too high. Ammonia will cause most fish alot of problems and so can nitrites. Nitrates don't cause as many problems as long as you do regular and frequent water changes and they remain low.
I only have read one article that suggested that the Flourish Excel caused a fish death. It was a tank that had four rainbow fish but it is not definite that it was the cause. As for the small water parasites-I am not sure exactly what you mean. I do know that alot of times there are planaria in most tanks and if there are too many it means that they are feeding on too many nutrients. The best way I have found to get rid of them is by frequent water changes and gravel siphoning. They don't do any harm to fish but they are a sign that a tank needs to be cleaned more frequent. There will always be a few but if there are too many then just do more tank maintenance.
Maybe you should try cycling your tank with just a couple of black skirt tetras and see how they work out. I have done this several times. They have always been very tough little fish. Of course still watch that ammonia and nitrite level and be sure to still do water changes to keep things under control.
Just be patient and I think things will get better in a few weeks. As soon as your ammonia and nitrite levels are at 0 then establish a weekly water changing schedule and your fish should do fine. Just don't add too many too fast and overload the bio load too fast, even after your tank has cycled. Also, please don't feed too much food especially while your tank is still cycling since this along with fish waste will cause too much for the bacteria to handle.
Best of luck!
Karen