how to know when tank lacks oxygen?

Just ouf ot his curiosity, saw a oxygen lack can kill fish post.
If you lack oxygen, how can you tell? And what can you do about it?

 

Often times the fish will be visibly gasping for air and hanging out at the water line.

 

so what can i do to prevent that?

 

Add more powerheads to cause alot of surface agitation. Overflows work well. Skimmer will help as well, since your injecting oxygen bubbles into the water

However that being said, not to sure what your options are with a biocube.

 

Make sure the water is turning over enough (enough water flow). Power heads are very good for that.

 

Best way to know if there is a problem is to get an ORP meter, other than that all you can do is look for signs that there might be a problem. You can prevent it by running a large skimmer combined with leaving the tank / sump uncovered and have plenty of surface agitation from powerheads and fans. I have a fan that draws air from the top of my tank and pushes it down behind the tank to the sump area as well as 2 fans blowing over the surface of the DT's water.

~Will.

 

can i get those 10$ machine that create air bubbles?

 

You can, but for about $15 you can get a powerhead. You can even put an airtube up to the powerhead to have to make bubbles AND flow.

 

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I already got a extra power head, oo but good idea, I can buy the air machine things, and put the cord around my power head, and make cool air bubble effect!

 

If your not having problems, there's no need to go out and buy equipment you don't need. If you have a skimmer, that really helps and if you have an open top and good surface agitation, you should be fine. You can also lower your temp a little, cooler water holds more O2. A sump, skimmer and refugium are a knock out punch for this. The skimmer by definition mixes water and air, the refugium will return O2 to the water through plant respiration and the overflow mixes water and air. IMO, this isn't a big problem, most people have no problems with dissolved O2, and if you do, it's easy to fix.