Missing Fish

When fish go missing, there are a few explanations.

They could be alive and in hiding - have you checked inside very ornament and plant
They could have died and the bodies are caught up in some decor - again, have you checked everywhere
They could have died and the bodies eaten
They could have jumped out of the tank - fish can get through the tiniest holes

Check inside every piece of decor and plant and behind an internal filter if you have one in addition to the new external. If you still can't find them, look on the floor around, behind and even under the tank stand. If you have a dog or cat, a fish could be inside them.
Does the external have a cover over the pipe going to the filter - the fish could be in there if they can get up the tube.

When you say you tested the water condition, did you check the ammonia and nitrite levels? The main cause of deaths in a new tank are ammonia/nitrite poisoning and fish that were already sick when you got them.
The new external - is that running with the original filter or did you replace the original?
Did you cycle the first filter with ammonia, use some already cycled media from another tank or set up a brand new filter and get fish?


Sorry for all the questions but the more info you can give the easier it is to narrow down what has happened.

Glad to hear you found them.

Was it the external filter they were in? If it is, you need to do something to stop them getting in there again. One thing you could use is a piece of sponge. You need a cubic shaped filter sponge, cut a slit in it and slot it over the end of the tube that takes the water out of the tank. The water will pass through easily, but the fish won't.