2 Swordtails Dead In A Week

[TropicalDan1]

I've got a 70L tank with (or rather had!) 4 Swordtails, 1 Male + 3 Females and a small Pleco.

The tank has only been running for 3 weeks but I didn't do a cycle. I added API Stress Coat & Stress Zyme then left the filter running for 3 days. Went to Pets at Home (Sadly the only place stocking fish within travelling distance due to no transport) and the test readings were fine.

I bought the Swordtails and they seemed fine for the first 10 days until the Male died, followed by 1 of the females last night.

I also do a 10% water change every other day.

Went back to P@H for another test today:
Ammonia - 0.5ppm
Nitrite - 0ppm
Nitrate - 0ppm
Temp - 26c

Not sure if it makes any difference but I have some 'Spider' plants behind the slate, the roots are underwater but most of the leaves are floating.

Any idea what may have caused the fish to die or is it likely they were ill before I got them?

 

[attibones]

Your fish died of ammonia poisoning. Currently your ammonia is at fatal levels. Your water changes are neither large enough nor frequent enough to preven ammonia poisoning. Your tank is also not ideal for this species because they need a fair bit of room (especially males, if you ever have multiples). They are fairly active fish. So, because your filter is too immature and you had too many fish to mature it, your fish died of ammonia poisoning. Kindly consider returning the remaining fish and doing a fish-less cycle. You spend less money on fish this way. You'll also save trips to and from your water source as you won't need to do as many water changes while cycling.

 

[N0body Of The Goat]

If you have not since posting this thread, do a ~95% water ASAP.
 
If you do not have a testing kit of your own and you are "fish in cycling", you should be doing ~50% water changes daily.