Mystery Otto Death

[MDK500]

I have a 15 gallon, high-tech planted tank (shown in first picture) that has been running for 5 weeks. water parameters are as follows: Ammonia 0 ppm, Nitrite 0 ppm, Nitrate 0 ppm, and pH 6.5. Yesterday one of my three ottos was continually swimming quickly to the surface, flipping over, and breathing from the surface then swimming quickly back down and grazing the plants for algae like usual. Today I found him dead. Now another Otto is doing this, and I do not know why. Other tank mates include 10 ember tetras (none of whom are doing this), 4 Amano shrimp (also acting normal), and 2 SAE's (also normally behaving). It seems only the Otto's are behaving oddly like this and a death has occurred of the first one that started doing it. There is no lack of oxygen, my plants pearl constantly and I do 30% water changes every three days.
So does anyone know why this is happening? Are they sick or have a parasite? Below is a picture of the tank and two pictures of the odd behavior.

 

[Sab_Fan]

how long did you have the Otos? in my experience, new Otos either die within a week, or they last for years . . . they can be a bit fragile until they are established, but once established, I have had minimal problems

 

[dpk2313]

yeah its sort of like the longer you've had them the longer you will have them If that makes sense
is there enough algae or food for them to eat and what is your temp?
amazing tank btw

 

[MDK500]

how long did you have the Otos? in my experience, new Otos either die within a week, or they last for years . . . they can be a bit fragile until they are established, but once established, I have had minimal problems

I've had them for about 3 weeks now.

yeah its sort of like the longer you've had them the longer you will have them If that makes sense
is there enough algae or food for them to eat and what is your temp?
amazing tank btw

There is enough algae, they're pretty fat. Tank temperature is 80.

 

[dpk2313]

I dont know we need Sherlock Holmes

 

[MDK500]

I dont know we need Sherlock Holmes

Sure sounds like it...

 

[Sab_Fan]

I have also found I have trouble keeping more than 2 in a small tank . . . whenever I add them to a 10-15G tank, I usually start with 3, and after a week or so I'll end up with 2 - - or maybe even just 1 - - that survive and then last for years . . .

so if you still have one left, that might be the survivor that lasts . . .

 

[MDK500]

I have also found I have trouble keeping more than 2 in a small tank . . . whenever I add them to a 10-15G tank, I usually start with 3, and after a week or so I'll end up with 2 - - or maybe even just 1 - - that survive and then last for years . . .

so if you still have one left, that might be the survivor that lasts . . .

Yeah, that sounds like the situation I'm having... but I still have two left, although one is doing this surface breathing thing and may die like the other one did.