60 L To 200 L Tank Change

If it would be possible, the best way to get bacteria in the new filter would be to transfer some media from the 240 litre's filter to the 30 litre's filter, and put the media from the 30 litre filter into the hole left in the 240 filter. The problem with just setting up a second filter is there is nothing to make the bacteria move into the new filter in any great numbers.

Moving substrate will help. There are many micro-organisms other than the filter bacteria which live in the substrate so seeding them with 'old' substrate will get them off to a flying start as well. The biofilm on any decor you transfer will hold a host of bacteria too.
And of course live plants use ammonia as fertiliser so they help as well.

Moving the cardinals across first is fine, though once you add the betta that will be quite a big addition in terms of bioload so you would need to monitor ammonia and nitrite twice - first after moving the cardinals and then again after adding the betta.

Cardinals might or might not work with a betta. They are compatible with the higher temperature required by bettas but they may nip the betta's tail. Or the betta might turn out to be on the aggressive side - there is no way to tell from the behaviour in the shop - but if the cardinals and betta don't get on, you do have the option of moving the cardinals back to the bigger tank.

To be honest bettas are better (sorry!) on their own. They are solitary fish and don't need - or want - tank mates. I have a 26 litre tank with just a betta and a nerite snail.

The other problem is finding fish that will be happy in a 30 litre tank. For example, cardinal tetras need a tank at least 60 cm long, and most 30 litre tanks are smaller than that.
The fish that would be happy in 30 litres are all small which could trigger the "food!!!" instinct in a betta. Maybe they'd be too big to actually eat but the betta chasing them trying to eat them would stress such small fish.


The other alternative would be not get a betta and get some small fish - for example endlers (males only) if the water is hard, or one of the Boraras species if the water is soft.

Hi again Sue

Set up tank on Tuesday as we agreed and put 3 small Corys in with a few shrimp.

Feeding very lightly ie 1/2 wafer and a few grains of micro pellets, and removing uneaten wafer.

Readings
22/3 TAN 0.25  (API), NO2 0.03 (Nutrafin), NO3 n/r (Nutrafin)
23/3 TAN 0.25, NO2 0.05, NO3 n/r
24/3 TAN 0.2, NO2 0.2, NO3 20
25/3 TAN 0.35, NO2 0.2, NO3 10

Am I ok here? Don't want to hurt the fish.

Regards, John

Thanks Sue, I'll get on it.

John

No, leave it set as NH (NH3 + NH4). This measures ammonia/ammonium as nitrogen plus hydrogen - N plus H - which is what our home test kits do. The other entry is for when the measurement is for just the nitrogen (N) part of ammonia and ammonium.