Sorry, first time I've seen this thread. Very amazing to have nitrates at 40 ppm with a 30% water change once a month. You must be doing some things right to keep your pacu alive for 27 years. I've only had my pacu for 17 1/2 yrs. Pacu are very sensitive to nitrogen products. Any ammonia or nitrite in the water, and my pacu would gasp. Change out enough water so there is no ammonia or nitrite (if there is any), even if you have to do several water changes. After fishless cycling my current tank, the only time I had an ammonia reading was when I fed the pacu copious, unlimited amounts of watermelon. Pacu are extremely messy eaters, and their water can quickly get fouled with food debris. My pacu get fed an exclusive diet of algae wafers to keep the water cleaner as their big tank is still not ready for them. Amping up your mechanical filtration should help with clarity and doing more water changes. My experience is that you cannot do too many water changes when it comes to pacus.
I belong to a pacu forum on Facebook. Some of the members write that enlarged lower lips is an oxygenation problem, and increasing aeration in the tank will help.
There was a time that I knew the names of many medications and what conditions they were used for. I run a UV sterilizer on the tank, and will never ever run a tank without one. The redox potential boosts fish immune systems. I haven't had any fish medications for 15 or 16 years.
I discovered this summer that my pacu do best with lower nitrates. I keep nitrates below 10 and change enough water to get nitrates between 0 - 3 ppm. If the nitrates get to 20 ppm, one of my pacus just doesn't look well. I do daily multiple water changes.
I noticed a lot of bubbles in your pictures. Could be an excess of protein debris in the water. The only fresh water protein skimmer I know of is Clarity CL-3. However, there are DIY foam fractionators, and
duanes
is an expert on that.
To summarize:
- increase mechanical filtration
- consider just feeding algae wafers until your pacu is in bigger housing
- more aeration
- consider an UV sterilizer (I have a 40W UV sterilizer on the return end of an FX-6) UV sterilizers are peace of mind for me
- water changes, water changes, water changes - start at keeping nitrates below 20 ppm