It looks like ich to me. Clowns can be an issue to treat as they are a scaleless fish, They are also somewhat sensitive ro Ich meds, so read labels on any med you decide to try.
Ich has a life cycle and not many meds can kill Ich in all of its stages. The speed of that life cycle shortens when the temp is higher. They nornmally have an upper temp. limit of 30C which is 86F. So make sure you do not get above 89 for sure and a degree or two lower should not make a hug difference.
Heat alone is often not enough to kill Ich. It comes in different strains which can be more or less sensitive to a given raised temp. The one thing that is sure is the life cycle gets faster the higher. Not all fish can tolerate the temp you reported.
Next, mit fish whoch get Ich and survive it develop an immunity gainst it. This is not permanet but I will last for some time. This is one reason why some fish in a tank may not get it. Unless this recovery had happened during the time you have jad the fish, there is no way to know in advance if any of them arrive to you with that immunity in effect. Usualy we find out when Ich hits a tank and wee see which fish do not seen to be affected.
Here is the good news, The Google AI actually gives proper information re treating clowns with Ich. Basically, you start with elevated te,mp. and use salt. If that does not help then you need to move a medication treayment. As I wrote above, they warn about clowns being scaleless. Do a Google for "best ich treatment for clown loaches" which should get you the AI info which you can trust.
You then should do some research into all the species in the tank before yo try salt as not all fih cantolerate it. Some plants will also not be happy. While doing the salt and heat you have time to research Ihc meds and determine what they suggest re xlowns/scalelss fish which is usually will be one of three options:
1. Safe to dose according the the medi directions.
2. Needs ti be used in a reduced dise which they wikk suggest.
3. Do not use at all.
It is important when mdeicating fish whether with something more natural like salt or using a chemical or midecation treament that you follow the directions. Usually trying to makes changes on your own doesn't work out well.
The google AI gives some med suggestions in this vain if I alter how I ask and that will give you a starting point re a few meds:
Ich-X by Aquarium Solutions is a highly effective and safe medication for treating ich in clown loaches and other freshwater fish. It is recommended by many aquarium enthusiasts and professionals for its efficacy and compatibility with various species, including sensitive fish, shrimp, snails, and even live plants.
Other effective options include:
Rid Ich Plus by Kordon:
This medication has been successfully used to treat ich in clown loaches, with no reported casualties.
Maracide by Mardel:
This medication is available at PetSmart and has been used effectively at half-strength to treat ich in clown loaches.
Quick Cure:
This medication is a cost-effective option that contains formalin and malachite green. It is effective at treating ich but may require multiple treatments to eliminate all stages of the parasite.
However, there are other options than the above so look beyond the 3 above a bit before you chose one. You may prefer to start with a med/chemical treatment rather than salt. If so still keep the heat elevated. Finally, Ich will spread to other fish n a tank. So The one thing the AI got wrong on the medication answer was to move the infected fish to be treated in a hospital tank. I do not recommend this. Treat the whole tank as is.
