New Aquarium Which Fish Are To Be Next

Hi Mick 

Did you cycle the tank with ammonia before getting fish or are you doing a fish-in cycle? If it's the latter, you can't get any more fish until you are sure both ammonia and nitrite stay at zero.

And I hate to be the bearer of bad news, but clown loaches are not suitable for a 180 litre tank. They need a tank with a base at least 180 x 60cm, and a tank with those measurements is going to be at least 500 litres. They grow to over 30cm long. Yoyo or zebra loaches are more suited to a 180 litre tank.

Having said that, tank mates for clown loaches just need to avoid slow swimming fish and those with trailing fins as clown loaches are apt to nip them. Any shoaling fish that grows big enough to avoid being eaten by a 30cm long fish would be fine.

Clown loaches live a very long time. The most famous clown loach, Marge, died aged 20 years.

Don't worry, everyone was a new starter once, even me  And a lot of shops/tank manufacturers give some terrible advice.

Getting the water tested before you got fish would have given you results for plain tapwater. With no fish to create ammonia, it should have been perfect. Once you put fish in the tank they would have been excreting ammonia. With no bacteria in the filter this would have built up. But with four juvenile clown loaches in 180 litres, it would take quite a while to build up to dangerous levels.
Have a read of this. It explains what happens when fish are added to an uncycled tank, and what you need to do. The good news is that with just the four fish, your levels will take quite a while to become dangerous. But you do need a test kit to monitor ammonia and nitrite so you know when they do become dangerous. Liquid reagent test kits (the ones with bottles and test tubes) are more accurate than the strips which you dip in water. They are cheaper on-line.
In your case you have an added reason to keep an eye on your tank water - clown loaches are very prone to developing a disease called whitespot (aka ich) when the water is the least bit iffy. Watch them for small white spots that look as though the fish has been sprinkled with salt.

Once your ammonia and nitrite stay at zero you can think about getting more fish. But not many. You will only have grown enough bacetria to take care of the waste from 4 clown loaches. If you add too many new fish at one go, the bacteria will be overwhelmed and you'll have ammonia and/or nitrite showing up.

No need to feel embarrassed. You would expect a fish shop to know what they were talking about. Unfortunately, many of them don't have a clue. They are only there to sell things not give good advice