If you're keen on tetras, then the x-ray tetra is a possible option for you - its requirements are 2-20 German degrees hardness (which equates up to 357 ppm / CaCO3), whereas harlequin rasboras' range is 18-215 ppm / CaCO3. The main issue might be whether the x-ray tetras would fin-nip the gourami - I've read mixed reviews as to whether they're fin-nippers. I wouldn't have trusted my own x-ray tetras with gourami - they tended to take a bite out my cories' tails when stalking them to avail of any extra food foraged up. If you wanted to take a chance on this combination, then best to ensure a large shoal with more females than males.
Guppies have a tendency to do the same with any fish with flowing fins or fancy parts on them, and male ones attempt to mate with such, so, although they suit your water hardness, may not be a wise combination with gourami.
As well as bettas being soft-water fish, it's very hit-and-miss as to whether they will tolerate any tankmates at all - so, between these two issues, not a risk worth taking. One option if you're keen on a betta might be to keep it on its own in a separate tank, using reverse-osmosis water. Pearl gourami are indeed a good option for the feature fish given that they can manage water 2-30 German degrees hardness.
Nice tank. I (and likely others) have some thoughts re your potential choices. I can't reply properly just now but, in the interim, can you let us know what your water hardness is in CaCO3 or German degrees hardness (as this will help work out which fish are compatible with your water); assuming you're UK-based, those figures ought to be available for your postcode from your water company website.
I have a 180litre tank with a under cabinet filter.
I have started my my collection and Plan on introducing new fish every week.
My plan is to have something similar to the list below. I have done a lot of research but would appreciate the opinion of some experts.
So I currently have: 8 danios 3 bristle nose catfish
What I am thinking of getting depending on advice 6 harleighquins 6 swoardtails Tetras but need to do research on which type don’t want fin nippers Guppies Possible shrimp allthough understand That a lot of things like these as a snack. Would like a feature fish but nothing to big, from what I have read a Betta (fighter fish) should be fine with what I have as long as I don’t get any fin nippers and only one. Other option is a dwarf gourami or both if they would be ok?
I think varying the diet is a really good place to start, and I will definitely incorporate a fasting day per week. I hadn't thought of pre-soaking the pellets, so I am going to start doing that as well going forwards.
Sorry to read about this. It sounds as though the cherry barb is indeed suffering from the effects of eating, possibly with the food pressing on its swimbladder and causing it to malfunction. My advice would be: * feeding less at a time but more frequently (eg if you have scope to feed the same amount to the tank per day but split it into separate servings spread out across the daytime); * pre-soaking any pellets/flakes so that it sinks and to prevent the fish taking in air when they eat; * varying the diet so that it includes veg such as chopped pea (shell off pea, each half chopped into tiny morsels) and frozen/live food a couple of times a week; * possibly a fasting day per week. Hope that helps.