This is my first post here, although not my first post on this site. Kept goldfish until lately, so posted there.
Here goes.... Bought a new setup a couple of weeks ago, trigon 190 litre corner unit, fluval 406 filter, etc etc.
Luckliy I was able to carry out a fishless cycle, using my media from my recently retired goldfish tank, so cycling was a lot easier than last time.
Currently my ammonia is 0, my nitrites are 0 and my nitrates are about 20 ppm.
My parameters have been stable, even introducing 6 young tropicals last Sunday....3 dwarf gouramis and 3 clown loaches.
Now the problem, the gouramis seem well settled in their new surroundings, but the clowns with the exception of the first day have basically gone AWOL.
Perhaps I should mention the tank is heavily planted with live plants, and supported by bogwood with a little stone, the sandy substrate has a layer of fertilised soil medium below it, which had no effect on my normal pH.
I think its possible the clowns are hiding under the built in filter Heater box.....(which incidentally is being decommissioned this weekend, now the canister should be seeded with the beneficial bacteria.)
Don't really want to loose my plants or bogwood, so are my to assume that the clown loaches are going to be strangers in my tank, one thing that does bother me, is I seldom see them scavenging, or even eating at all, when the do appear they look healthy and seem very much OK.

Gosh, 84 people read this,and no one as ever kept one.

Welcome to the dark side
Few problems here I'm afraid. Firstly the clown loaches...probably not the best choice if I'm honest. Kind of the goldfish of the tropical world in many ways. They can grow up to 40cm, and have a ridiculously long lifespan - they'll quite happily keep going for 20 years or more, and I vaguely remember reading somewhere they can live as long as 50 years!! Also they need a minimum of 500l/6ft. So I'd recommend rehoming them and finding something more suitable for your tank.
The dwarf gouramis should be fine in terms of tank size, but they are territorial (especially the males) so shouldn't be kept in groups other than a male and female pair. Females are rarely seen in shops as the males are much more colourful, so yours are most likely all male. I'd rehome at least two of them.
Do you know the hardness and pH of your water? This is important as different fish have different requirements. Hardness (GH and KH in German degrees) you should be able to find out from your water supplier's website - there should be a page where you can type in your postcode and get a water quality report for your area. pH will be there as well, but this will be the reading straight from the tap and it can change when the water is left to stand. So I'd recommend testing it yourself after leaving a sample of water to stand for 24 hours. You may find that the water chemistry isn't suitable for the gouramis.
What are you doing with the filters? If you are just going to run the two filters together for a while then decommission the old one, that won't work. The bacteria are happily settled in the existing filter and won't just decide to get up and move to the other one. What you need to do is remove the media from the old filter and put it into the new one - some squashing and cutting may be required.

OK, thanks James, with regards the built-in unit, well that was decommissioned today, I used all the media from the old filter and reintroduced to the new....actually the same media as been used in several filters and only occasionally lightly rinsed in old changed aquarium water, it was not left to stand for more than 5 minutes, so I'm comfortable the filter will work fine.
Agree the clowns do grow bigger than what I first believed, but we have a very good swopping website locally that usually accommodate large fish, there is always someone looking for fish that are large, the same as there's always someone that as a bigger tank than yours, lol.
Regarding the gouramis, they seem fine, I have certainly checked out all parameters, they meet the necessary requirement for gouramis, and they seem fine. I will monitor carefully the interaction between them and act accordingly if problems arise.
But thanks a lot, its kind of you to reply, and I will certainly try to get this right.