Guppies dead & Mollies nervous

greeners

Im new to this so bare with me!
We have a 7mth old 48ltr freshwater tropical tank - no live plants - have bog wood and rock - Current fish stock - 6 x-ray tetras & 2 mollies & 1 temperate shrimp

Temp is 27 oC and amonia is 0 only occasionally slightly raised to 0.25 Nitrite is 0 and trate is 40 (hope i got these the right way round!) PH is 7.5 ish
We do water changes weekly but recently a 6mth old Guppy died it had had a curved spine for a while and then just died, we'd intorduced the shrimp about 2 - 3 wks before this Guppy died. we did a 40 - 50% water change on the day it died, and put in ½ a new filter pad. Then 2 days later bought 2 more guppies to keep the original mate company but then 4 days after the first death the 2nd 6mth old one died, then 1 of the 2 new ones seemed shy and not eating so we got some bacteria medicine (begins with an M) using this meant we did have to take out the carbon from the filter- however within 3 days that Guppy had also died. We thought we were in the clear then 4 days later the 4th and last Guppy also died. Throughout this we have done small water changes and always use tap safe and filter start.
We are gutted as we use the test tube tests and have never had high readings. The concern now is are we likely to loose more and we are totally unsure why this happened as no outward signs of ill health.

Old tetras are happy as usual now, but the mollies use to greet us every morning when its was feeding time - now they seem nervous and jumpy but all still feed.

Anyone have any idea's???

Byron

Welcome to Tropical Fish Keeping forum.

You have quite a few fish in a relatively small tank, 48 litres/12 gallons. The nitrate at 40ppm is indicative of this for one thing. I would not suggest going beyond the 6 tetra and 2 mollies and shrimp.

To the guppies, a deformed spine is often genetic and it happens. The Guppy may have brought something in with them. I won't speculate on disease issues as i do not have the knowledge.

Live plants would help, even stem plants or floating plants. Nitrates at 40ppm is considered OK by some but not by me. I recommend keeping nitrate below 20ppm, and in a balanced tank this is easily done via live plants and/or partial water changes.

Make sure a couple of the foods you feed are plant or vegetable-based for the molly. This is good for other fish too, but molly need it.

Byron.