4 angelfish died last night

Question
I have a 20gallon tank that has been only cycling for a week and a half. This is my first tank and I admit I made my fair share of mistakes. My first mistake was adding 4 fish in the same same day, 2 at a time over the span of 3 hours. I did let them sit in the water for 45min-1hour. Yesterday I added 4 more fish.

They are all young right now. I am looking into a 60gallon if I think I can handle it.

So now this brings my tank up to 4 Angelfish, 2 Balloon Mollies and 2 Plceos (one of my Golden Nugget Plecos also died last night. I assume it was not enough oxygen because of the new setup? But the other Pleco is fine, also a Golden Nugget but younger) making a total of 8 fish.

Last night I noticed that my Marble Angelfish and my Koi Angelfish were floating around the aquarium flapping their fins and moving their mouths. I tried looking up sleeping behaviors of Angelfish but I couldn't find anything useful. Right before I went to sleep I saw that they had made their way to behind the filter and were finally sleeping upright and in once place. I woke up to find them both dead, along with one of my other Angelfish (I don't know the name but here is a picture of it http://img184.imageshack.us/img184/2135/23ko9.jpg). Not long after that the other Angelfish I had pictures above was acting the same. It was flapping its tail and moving its mouth but just floating around the tank lifeless. I figured it was going to die just the rest so I put it in a cup with water and put it in the freezer. I read that was an easy way to do it and the fish didn't feel anything because it numbed their nerves.

So now my tank is down to my two Balloon Mollies and my Golden Nugget Pleco. The Pleco every so often goes to the surface of the water, it seems like he's getting some air but I really have no idea.

I tested the water prior to adding fish number 4-8 and these were my results:
Nitrate - 40
Nitrite - 1
Hardness - 300
Chlorine - 0
Alkalinity - 300
pH - 8.4

When I got the above test results my tank had been cycling for 4-5 days with 2 Mollies, a Pleco and a Marble Angelfish.


Prior to my fish dying and after I added the other 4 fish I got these results:
Nitrate - 40
Nitrite - 3
Hardness - 300
Chlorine - 0
Alkalinity - 180
pH - 7.8

When I got the results above I had 8 fish in my tank, they all seemed fine. They were all eating and swimming around.


Then last night after my Pleco died I tested it and got these results:
Nitrate - 40
Nitrite - 3
Hardness - 300
Chlorine - 0
Alkalinity - 300
pH - 8.4

A few hours after these test results the Angelfish started acting weird and slowly started to die.


I have not been doing water changes because I don't know how to do them. I just filled up a bag with tap water and I am letting it float in the aquarium before I do the water change. I don't even know if that is the right way to do it. Do I put the conditioner the Cycle in the bag or in the aquarium once I change the water?

I'm sorry for the long question, I wanted to make everything clear & detailed as possible but I probably just ended up confusing you.

O! One last question. Is there sand that is safe for freshwater tanks? Does it require a lot of attention to maintain the sand?

Answer
Hi Mike, thanks for your detailed question!

Sorry to hear about all the fish trouble. I think you're problem here (as you already know) is stocking the tank too suddenly, especially since it was new and not cycled. I would be very curious to know your ammonia reading. That is really the most important thing to test for (along with nitrite) when the tank is cycling. What it sounds to me is your fish have been suffering from water pollution problems. And the easiest remedy to that is water changes. Water changes can save the lives of fish when there are ammonia problems.
You're going to more trouble than is necessary for changing water. All you need is 1-2 one gallon pitchers, an aquarium siphon/gravel vacuum and a 5 gallon bucket.
Just start the siphon and drain the water into the bucket, make sure to gravel vacuum at every water change.
Then when you've drained out some of the water, dump that (outdoor plants love aquarium water) start refilling by getting your water conditioner (like stress coat) together and the pitchers. Try to match the facet water's temperature to your tank's temp. You can use a thermometer but using your hand works fine. Try to match it closest to your tank water, but a little bit warmer is fine. Never make it colder or you risk stressing your fish and making them suceptible to ick or white spot parasites.
Add your water conditioner as the pitchers are filling. I use a simple system where I let one pitcher fill (with water conditioner already in it of course-I use around 1/4teaspoon or close to that per gallon)then once that's filled, leave the tap running and set the second pitcher in there (already with conditioner also) while I pour the first one in the tank. Repeating this saves some time on refilling and has worked out well for years.

I think your problem here is simply because your tank is in the break in period and lots of water changes are needed to keep the water conditions under control. I'd do about 50% at least everyday for now if you still have fish left. And try to get an ammonia test kit so you can see how far long in cycling you really are.

As for the sand, a lot of people use playsand. But it must be washed and washed like crazy. And even then it may not be completely clean. But it looks nice and wouldn't be too hard to maintain as long as you don't have a deep layer (an inch to an inch and a half would work) I use a large grain sand in my aquariums. I believe its considered silica sand. It's very easy to get and keep clean, the larger grains means you can easily vacuum it and it won't cloud the water if its stirred around. You can also read more about sand here:

      http://cichlid-forum.com/articles/sand.php

I really hope this helps, I think you'll get through this bad fish dillemma with lots of large water changes, once your tank gets established you shouldn't have anymore trouble either.

Best of luck!
Karen~