Hi fellow members ,
I have a problem within my soil for my cactus, it's spring here in Australia and I've repoted my cactus in cactus and succulent potting mix , but in the last week when I water or disturb the soil there are quite a few of these flying bug type things that look very simalar to fruit fly , are these thing harmless or is there a treatment I can use to rid my cacti from these very annoying Things ??
Thanx

fungus gnats?
let the soil dry more between waterings
and /or top dress with diatomaceous earth

Uuug(
Ok thank you cool , also I have pebbles on top of the soil should I remove them so the soil can get fresh air ??

Letting the soil breath would help. Right now the pebbles are essentially acting like mulch.

To be clear, the fungus gnats are not a problem; they are of no danger to your cacti. Their presence, however, indicates that the soil is too wet; wet enough to be culturing fungi. So don't pay the insects any mind, just focus on getting the soil dry. Once that happens, the fungus stops thriving, and the gnats go away.

A lot of commercial succulent potting soils are almost all peat, with very poor drainage. Did you amend the soil in any way, or does it already contain a good amount of perlite or somesuch non-organic drainage booster?

When I brought the soil I didn't add any other product as I thought it needed nothing added as it was pacifically for cactus , if I make soil up myself am I to use a mix of river sand , perlite , and top soil ? ? Or can I just add something to this potting mix ?

A few questions. Are you using clay or plastic pots? Are you growing trichocereus or globulars? Are they seedlings or adults? Do you live in a dry climate or a humid climate?

Fungus gnats can be a problem if they get really bad and eat too much of the root system. Mostly with younger plants and seedlings. The best remedies for fungus gnats is A: Bacillus thuringiensis ssp. israelensis or B: dry soil. The first option is a product called Gnatrol (or other brand names with the species) You just water you pot with the stuff and it will kill off any gnat larvea. That stuff works awesome if your soil is wet most of the time. With dryer soils I've never encountered fungus gnat problems, but trichs love their water if it's hot and sunny while they're actively growing. So sometimes drying out the soil too much can hinder growth a little bit.

The pebbles will definitely retain water in the pots. I intentionally use gravel as top dressing for my trichs because where i am the soil dries out too fast without it. If you live in a humid place top dressings can be a bad idea though. It also depends on what kind of pot they're in.

And store bought cactus soil works fine for trichs, but it's not the best option. Even normal potting soil works for trichs. You don't need to be changing your soil mix or anything at this point. I would just wait till it needs re-potting before you go changing soil mixtures.

Maybe it's best if put up pics !! Also I live in nsw Australia so you could say a warm climate dry at times but not that humid !
Porcilen pots and I've removed the rocks !!

They are sciarid fly // fungus gnats. Very attracted to plants growing in peat - particularly indoors. It is their grubs that can eat through plants of ALL sizes, but especially seedlings. Basically stop growing in compost containing peat and your problem will be gone.