Neon Cardinals and Dwarf Gouramies Dying

[selfcurious6830]

Neon Cardinals and Dwarf Gouramies Dying​

Hi, I would be very appreciative if someone who knows about these fish could help me out.
About three weeks ago I got a 74L Ciano 80 fish tank and I circulated my tank for a couple of weeks with plants until I bought my fish last Friday on the 20th of May. I bought 7 Neon cardinals, 4 red platys, 4 male guppies and two Dwarf Gouramies. I took a good few hours to acclimatise them in their bags and I did everything the people at the fish shop told me to.
I had been feeding them every other day because they told me to at the fish shop (for the first week) and since yesterday (Friday 27th) I've been feeding them every day.
Yesterday, I did my first water change (they told me to change about 10% every week) but before I did it I noticed that one of my Neon cardinals had died and was floating on the top of the surface. I got a bit upset because I am a first time tropical fish keeper but my dad who has been helping me has a lot of experience and he reassured me that they could just have bad genetics because they are bred a lot, or they were sensitive and got too stressed when moving into my tank.
So I continued with the water change and I tried to match the temperature as best I could.
Later on yesterday I found another dead cardinal. Today, (Sat 28th) one of my Gouramies died, and another cardinal. I have become quite upset and anxious because I really don't know what I am doing wrong.
I think that I am feeding them the correct amount, and I wondered if they might have a disease but they seem to look fine.
The cardinals in the tank seem quite skinny and flat-bellied even though they have been eating.
The platys and the guppies seem to be healthy and show good behaviour. I'm just worried that the other Gourami might die.
I know that this is a natural process of tropical fish keeping especially as a first timer, but I just really want to know if I could be doing something better to help my fish.
The photo attached is the dead Gourami and Cardinal (I'm not sure how long they were dead before I found them)
Please give me some advice and thank you so much

 

[outofwater]

Hi, welcome, unfortunate circumstances. You need to test the water for ammonia, nitrites and nitrates. If you don't have a test kit maybe your local store can test water for you. From your message it wouldn't seem as though your tank is yet fully cycled, and that is most likely the reason for the deaths. What plants do you have, and what water treatment do you use? (dechlorinator)

 

[itiwhetu]

I am afraid you have just added too many fish to this tank all at once. The secret to a planted cycle is that you plant the tank to about 50% of the volume, then when the plants start growing add a couple of fish at a time over the next few months. It is important to test your parameters now to find out what is happening. Nitrite, Nitrate, Ammonia, and pH.

 

[Essjay]

(they told me to change about 10% every week)

At the moment you need to be changing a lot more water and a lot more frequently. Until you can test for ammonia and nitrite you need to change half the water every day. When you can test, change half the water whenever ammonia or nitrite read more than zero. After a few weeks, those readings will stay at zero, then you can do weekly 50% water changes.


It won't kill fish quickly but with a location of London you probably have hard alkaline water. The fish you have now need soft acid water. Going forwards, Can I suggest you choose fish which come from hard alkaline water as they will do better long term.