A 20g is way too small for them, now. When it comes to a larger tank for the clown loaches, we mean at minimum a 6-foot, but an 8-foot is actually what you need. Is this really possible? If not, or "maybe," you should re-home the loaches now before they are detrimentally affected by stress from the numbers. This may already be occurring, it is not possible to see until it is too late and the fish either turns aggressive or dies.
Loaches are highly social fish, and have an inherent need (programmed into their DNA) to develop an hierarchy within a group of five minimum or more. Think of it as serious mental issues developing.
The Giant Danio in a group of six or seven would fit this tank, but not with gourami; danios are active fish, gourami are sedate, and the two do not mix.
The Siamese Algae Eaters are another problem waiting to occur. Also a shoaling fish, but at six inches...I would re-home. Not a good match with loaches anyway. And the weather (dojo) loaches...also not compatible, these must have cooler water.
Oh how I do wish store staff had training, or at least the wisdom to do research before advising. We could avoid so much distress to fish and their keepers.