Head Looks To Have Had Sudden Fatal Inflammation

Was nine WCMM only
28lt Tank been running for 3 weeks
Started with Tetra safe start and Aqua safe
Fish have been very active and happy, lots of attempts to breed
New plant went in 4 days before the death
New stones from a clean freshwater stream 7 days before death
Snails noticed about 5 days before death
The death must have been sudden as I watch the fish a lot, and possibly less then an hour they were all happy
I noticed one floating and looking slightly bent backwards, however after inspection a large swelling with a small amount of blood within was noticed, they eyes also appered slighlty bulgy (see Photo)

Being a scientific minded person I would like to understand what has happened.

To my relief the others all appear happy this morning PHEW!

So, what is your ammonia and nitrite reading?

If its been going for 3 weeks using Tetra Safe start, which does jack, i dare say they are not good.

PS. I treated the water with protozin after finding the dead fish

the water gets a weekly partial change about a 3rd to a qtr change

toxic water would give an over inflammed head?

I screwed up my 1st batch of WCMM from bad water (had chloramine so evaparation failed) and none of those displayed this slightly popped head sympton

ammonia or nitrite can cause all sorts of issues, like i said, what do they read?

pH and temperature readings would useful too.

I am a hobbyist, and not well off.....sorry I dont have those readings. Besides WCMM are supposedly hardy and dont mind cold water (mine is room temp)

The other guys look active and healthy. I know what they look like when they are sick from ammonia, and they look fine.

I do water change weekly and use tetra water safe.

One suggestion from an aquatic store suggested a tumor or such like.

its possible, but, sorry to be blunt, but you don't buy fish before you buy a fish tank so you really shouldn't be without a test kit before you buy your fish either.

Local shops will usually test water for £1/£2 and give you the readings...we are all hobbyists so being able to test the water makes it a lot cheaper in the long run as we don't have to replace dead fish...which can be costly

Absolutely no idea what it could have been, fingers crossed it doesn't happen to the others.

I would be changing 50% of the water every 2 to 3 days since your tank is still very new the filter will not be dealing with ammonia or nitrite yet. I would also feed very little. gluck!

Thnx, I just did a water change, will do again in a couple days

i have looked at the test kits but they are expensive luckily my local(ish) shop can test water for free

that's very good of them!

API Freshwater master kit is about £18 on eBay, worth saving a few pennies for.