How to tell if you need to add oxygen to the water?

[duanes]

Is there a film building up on the waters surface? This could impede oxygen exchange, and if so encourage the fish to gulp water at the surface,
not a normal condition for uropthalmus
I believe this is your newly set up 75 gal, with only 1 fish, no?
so being a new set up, it may be going thru some "new tank" blips, growing pains, and set up adjustments, such as bacterial blooms, filter media bacterial population fluctuations, etc that could produce varying dissolved oxygen conditions.
As you can see in one of my photos, the flow is pointed "down" into the water column providing current across almost the entire 6 ft length, but the venturi port is placed near the surface to allow a lot air to be sucked into the port and pushed by flow into the tank where enough turbulence is created to break up surface tension that might allow film to build up on the air water interface, and impede oxygen exchange.

In your first photo the air-line tube attached to the venturi port of the power head looks quite long, maybe too long, and the port too deep in the water to allow it to successfully pull enough air to work properly, I only see a few tiny bubbles in the effluent of the power head, in the shot.

 

[Finthusiast]

Indeed there has been a sign of film I did a 50% water change two days ago and filled water higher than usual which is the main reason I believe I lost most of my surface agitation from my emperor. The air pump Is using a extra long tube right now cause I didnt take the time to make a custom cut piece for the tank yet lol just noticed he was showing the signs of possibly low oxygen so I just plugged in what I had cause better than nothing I thought also I do have them turned way down cause I wasnt sure if these “micro-bubbles” were going to cause any discomfort to Crash. Do you recommend I keep it connected to the powerhead of ahould I get a “bubble wand”?
Hey thanks so much for diving deeper into this question with me lol as I am loving to learn every bit I can to make sure I am providing the proper conditions for my fish!

 

[neutrino]

Ime a bubble wand/air stone should break up surface film and so should sufficient surface turbulence. Imo an Emperor 400 is a somewhat marginal filter for a 75 gal tank, probably okay for low stock or one fish, but...

I lean a little to the minimalist side for equipment in my tanks. I work more toward ecological balance and I don't add superfluous filters just to achieve some magical filter turnover number. Also, if filters are providing enough oxygen I don't add additional air sources, and I don't add power heads just for the extra current. All of this works quite well for me, my water is clear, nitrates are low, fish live a long time, all while I do large but no more than weekly water changes.

All of that said, back when I had them, I found that a single Emperor filter alone on a 75 gal tank was marginal to inadequate for my tastes, depending on stock level, and I typically added more filtration to them-- and that was with me filling them to the brim with media, poly fluff, etc, trying to make them as efficient as possible. (an Emp 400 on a 50 or 55 was fine ime)

Just to compare, I've found the 400 gal/hr Aqueon 75 filters, though smaller media capacity than the Emperor, is actually sufficient, also an Aquaclear 110 should be. This appears to me as due to the actual water volume moved with an Emperor being less than the Aqueon since the flow is split, part of it bypasses the media and simply pushes the bio-wheels. In other words, the Aqueon holds less media, but water passes it more frequently and outflow is stronger.

Once upon a time I liked the Emperors but I've come to see them as durable, but inefficient-- besides having nearly all canisters now, anyway. The Aqueons are more effective, though cheaper made-- at least vs. the older Emperors, I haven't bought one for years.