Signs of low dissolved oxygen levels?

[Maximus]

I have a 55 gallon tank with a HOB. I used to have the water level low enough to allow the water to fall into the tank to oxygenate, but recently I put an airstone in the HOB and raised the water level. It's a planted tank, and everyone seems happy. That being said, I don't own a DO meter, but am wondering if there are general signs I should look out for that indicate DO levels are too low? Lethargy in fish, things like that. Thanks

[Lennie]

Waterfall effect vs leveled up HOB does not seem to have so different levels really. Airstone addition is great!

Generally the problem with heavily planted tanks is, besides fish, beneficial bacteria and  plants also keep consuming oxygen during night time. In low oxygen environments, especially close to morning times, fish may starve for some oxygen. Also your stocking level may play on a role on this one too.

Generally, one of the signs I happen to observe is, fish being super inactive, trying to stay upper side of the tank and close to surface acting like betta geting a  gulp of air from the surface.

I think this video might help you to understand some of the concepts :

 

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Edited April 4, 2023 by Lennie

[AndEEss]

Water level should be high enough that you get surface agitation and disturbance across the top of the water. 

The water plunging vertically into the water is NOT what you want for optimal oxygenation. 

[Lennie]

On 4/4/2023 at 10:38 PM, AndEEss said:

Water level should be high enough that you get surface agitation and disturbance across the top of the water. 

The water plunging vertically into the water is NOT what you want for optimal oxygenation. 

Actually, both works. In the video above, waterfall one even reads higher oxygen content than the leveled surface agitation. Check the min 14

[Maximus]

In my experience, I get more surface agitation with the water falling into the tank vs. having it level. That could be not-great design of my HOB, though.

[nabokovfan87]

On 4/4/2023 at 9:15 AM, Maximus said:

That being said, I don't own a DO meter, but am wondering if there are general signs I should look out for that indicate DO levels are too low? Lethargy in fish, things like that. Thanks

Red gills, stress signs like gasping, something like otos, plecos, loaches you'll see it on them first because they are against the glass normally.

On 4/4/2023 at 12:54 PM, Maximus said:

In my experience, I get more surface agitation with the water falling into the tank vs. having it level. That could be not-great design of my HOB, though.

This is a super fun look at just how much water height impacts your tank.

More movement, surface exchange = more oxygenation for the tank.
 

 

[lefty o]

fish gasping at the surface will typically be the first real obvious sign you have an oxygen problem.