Female Pearl gourami w/ Cloudy eyes and red spot

[Lvkas]

Hello everyone, 

I’ve had this pear gourami along with 3 others, 1 male, and 2 females for a little over a year now. I’ve posted about this particular female in the past as she’s had several bouts of cloudy eyes - she’s the only gourami to ever have any issues and based off of the tank dynamics she is clearly the bottom of the social hierarchy. The 3 females have relatively large abdomens but they’ve been like this for 9+ months, the group has spawned in the past, and I see them regularly poop so I would assume they’re not constipated?  

This time she has a red spot on her underside near the back of her body that is visible on both sides which leads me to believe there’s something internal that is appearing symmetrically on both sides of her. 

The tank is a top fin 40g tank that has a rainbow shark which never bothers any of the fish in the tank, 6 bronze corys, 4 otos, a BNP, the 4 Pearl gouramis, and one lone barb that terrorizes all of the female pearls pretty much equally. 

This barb has been in the tank the whole time and has killed all of the other 11 barbs that were with it before the gouramis and corydoras were added. 
 

I am in the process of setting up a 40L for the barb to move into as I know the stress is likely a casual issue for this pearls health issues but I was wondering if anyone could give me some insight as to what it is? Internal parasite? Abrasion from the barb? It’s the first time I’ve ever seen a spot like this on any of my fish in any of my tanks and am unsure about how to approach it.  
 

Any help would be much appreciated 

Water Parameters:

• pH - 6.4
• Nitrates - 0-20 depending on if I recently culled the floating plants from it that week
• Hardness - very hard 300+ 
• Nitrite - 0 every time
• Ammonia - 0 every time 
• KH/Buffer - low 0-40 on any given week (there is a bag of crushed coral in one HOB to supply some buffer)
• Water Temperature - pretty much always around 74-76 depending on the temperature of the house currently 

Edited June 5 by Lvkas
Forgot additional information

[Colu]

Your water parameters are fine what could be going is this fish is being bullied and under constant stress weaken immune as its bottom of the pecking order leading to secondary infections what I would suggest if you can is quarantine this fish and treat with aquarium salt 1 table spoon for 2 gallons for 1 week @Lvkas