Just added 2 new catfish how long should I leave them before I change gravel

Hi everyone I have brought 2 new catfish new sure which type they both different tho I shall upload photo but have brought new gravel at the same time I was wondering weather I have to let them settle in the tank first before I change or am I ok to change later tonight.
Thanks in advance

How long has your old gravel been in? If it is a long time and you disturb it you will release all sorts of nasties into the water which may be detrimental to your fish. Are you just adding gravel or are you changing it? You have a khuli loach there and they prefer sand so they can burrow into it, also your catfish would probably be better off in sand but a fine gravel is ok.

I didn’t realise that about the loaches I was torn between sand or gravel but picked gravel as that’s what I had before and yes the gravel has been for a while how should I change it with upsetting the fish the gravel I have brought is finer than what’s in there now tho or am I better off getting sand instead ?

If you haven't opened the pack of gravel yet, it would be better for the fish if you took it back. Sand is much better for kuhli loaches and other bottom dwellers. Play sand (Argos and B&Q if they'll sell it at the moment as it's 'non-essential') is the cheapest and it is safe for fish; it's just got a lot of dust in so needs washing well.

As for changing the gravel, prepare the replacement in advance, you don't want to be stuck washing new sand or gravel in the middle of changing it. Turn the filter and heater off, remove some of the tank water and put it into a largish container of some sort. Catch the fish and put them in the container together with any decor. Then remove the old gravel - it will make a mess so you'll end up having to remove all the water. Put the new substrate in. If you have live plants, put some dechlorinated tap water in, then plant the plants. Then put the rest of the decor in, then the fish. Then just fill the tank back up and turn everything back on.
You will have lost bacteria in the old gravel so test the ammonia and nitrite daily until you are sure they are remaining at zero. If they go above zero, do a water change to get them down.

That’s brilliant thank you I will take the gravel back and get sand am assuming sand is ok as I have 4 guppies 5 tetra an angel and the 3 loaches

Play Sand will be fine for them, good luck.

What are the tank dimensions (length x width x height)?

What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).

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The catfish looks like a juvenile Synodontis petricola or something similar and they come from Lake Tanganyika, which has very hard water (GH above 400ppm). They should also be kept in groups.

The Khuli Loach is a soft water fish, as is the bristlenose catfish. Angelfish and tetras are also soft water fishes.

If you wanted to change the substrate you should have done it before adding new fish.

I would not change the substrate for at least 1 (preferably 2) weeks because the stress of being bought, caught and put into your tank, and then having the substrate changed, could be too much for the new fish.

One other thing for your info, when you put in the sand don't be tempted to have a mix of sand and gravel as the gravel will rise to the surface with the sand underneath and you will have gained nothing.