Golden sucker loach

How many gallons is the tank please?
How many fish and which type?
Water stats in ammonia, nitrite, nitrate, and ph?
Does your substrate have rough edges?

 

Can you post your water results please. As the strip not telling me anything.

Don't know much about the loach you keep But the red spots or patches could be due to your substrate. They can get cuts and wounds if the substrate is sharp.
Might be better of changing the substrate to sand.
Do the corys show any marks on there noses or mouths. Also sharp substrate can wear there barbals down,

 

Are you sure there red spots and not red patches?

 

When did you notice them?

Red spots can be bacterial, septicemia, parasites. Or they could be caused throw digging in sharp substrate.

 

If he gets more spots come back to the thread, or
If he starts acting out of charactor, or the spots show no signs of healing.

 

Good Luck.

 

How long has the fish had the red spots on its nose for?
How long have you had that fish for?
Did you add any new fish within 2 weeks of the spots appearing?

How often do you do water changes and how much do you change?
Do you use a gravel cleaner to suck the gunk out of the substrate when you do water changes?
Do you dechlorinate the new water before it is added to the tank?

How often do you clean the filter and how do you clean it?

I saw the test strip but without a colour chart to compare it to I have no idea what the results are. What were the actual test results (in numbers)?

It looks like physical damage that might have been caused by the fish swimming into something or grubbing about in the gravel. As Wilder suggested, monitor and if it gets worse then post another picture with updated information.

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A couple of points about your tank. You have a water lily by the filter outlet. Water lilies don't tolerate water getting on the top of their leaves and rot in humid conditions. Is there any chance you could move your filter to the other side of the tank, or move the plant to the other side, preferably the filter tho so the plant doesn't get damaged now it's starting to grow.

There are 3 Swordplants in the tank near each other. These plants can get pretty big and will eventually shade each other. If you spread them out a bit more (move them further apart), they will do better because they will have more room to grow and get more light.

On the left side of the tank you have Ambulia and then Hygrophila rubra? in the back corner. The Ambulia will grow to 3 or 4 foot long, whereas the Hygrophila usually only grows to about 1 ft. As the Ambulia grows you might want to take some cuttings from it and plant them along the back, and when the H. ruba grows take cuttings and put them at the front. Then you will have taller plants at the back and short plants near the front.

All in all tho the tank looks quite nice

 

I don't know what to tell you about your problem but I will tell you....Beautiful tank!!