Apistogramma Rests on Aquarium Floor

[LukT]

First post here so apologies in advance if this is in the wrong section but I've struggled with researching this so figured I'd ask for some advice.

I have a pair of apistogramma macmasteri in 20 gal that have been doing well for nearly 2 years. Just within the past week or so my male has suddenly undergone what I can only really describe as having lost his swimming abilities. All day he just sits on the substrate occasionally scooting around to different spots. When it comes time for food he swims up to the top and eats, but sinks like a rock and appears to breathe very heavily after such an endeavor, and it takes a couple minutes until his breathing returns to normal.

I observed it for the first few days and now have moved him into a hospital tank with that I have only dosed with aquarium salt. He still eats with no issues and comes out for food. He also doesn't appear bloated as far as I can tell. I will say that his colors are far duller than in the past, which is exceptionally evident in the stark color contrast between him and my other apisto.
No other fish in the original tank have had any issues.

Water parameters that I tested were:
Ammonia - 0
Nitrites - 0
Nitrates - 40 (did a large water change right after testing)

In my time fish keeping I've been lucky enough to avoid every really having illness with my fish, so I'm far from an expert at identifying this. Can anyone lend a hand? Is there any medicine that would help in a situation like this?

I will respond with requested details, photos, etc. in the morning but I figured I'd get this out there so I could receive advice by morning.
Thank you all.

 

[Colin_T]

Post a video of the fish on YouTube, then copy and paste the link here.

If it's still eating well but no longer able to remain buoyant in the water column, it could have a swim bladder issue. There's no cure for swim bladder issues. Due to the fish being a bottom dweller that lives in pairs in caves, a swim bladder issue is less of a problem compared to a schooling fish or a fish that lives in the upper part of the water column.

 

[GaryE]

It isn't a good sign, ever. If you have harder water, he may be timing out from old age. People underestimate the physical cost of life with minerals in the water for a fish from extremely soft water like a macmasteri. It shortens their lives.

If it isn't that, it could be just one of those things that happen. It can be an infection, an internal organ issue, etc. Without knowing, there is no med you can try. If he were one year old, I'd suspect a bacterial infection, but that doesn't mean it could be cured.

 

[LukT]

Post a video of the fish on YouTube, then copy and paste the link here.

If it's still eating well but no longer able to remain buoyant in the water column, it could have a swim bladder issue. There's no cure for swim bladder issues. Due to the fish being a bottom dweller that lives in pairs in caves, a swim bladder issue is less of a problem compared to a schooling fish or a fish that lives in the upper part of the water column.

It isn't a good sign, ever. If you have harder water, he may be timing out from old age. People underestimate the physical cost of life with minerals in the water for a fish from extremely soft water like a macmasteri. It shortens their lives.

If it isn't that, it could be just one of those things that happen. It can be an infection, an internal organ issue, etc. Without knowing, there is no med you can try. If he were one year old, I'd suspect a bacterial infection, but that doesn't mean it could be cured.

Here are the links to videos:

As you can see, colors are very dull but I can't seem to identify any other issues.

Once this problem developed in the main tank he never left his cave aside from coming out to eat. How long do you think I should wait to see if the salt has any benefits? Otherwise would it be ill advised to transfer him back into the main tank if nothing further develops in a week or so?