Fish are gasping for air

[exterminator]

In the morning I see all my fish swimming at the surface gasping for air. It started to happen after I added 7 additional fish.

I have a moderately planted tank. Temperature is 26C. Rena XP2 canister filter. Output is well bellow the surface, so no agitation. Lights are on for 12 hours. Tank is about 3 month old. No supplemental CO2, just add 10mL of Flourish Excel daily.

Why is it happening? Is my fish load to heavy? Should I start using airstone?

[unclefahaka]

I'm not a fish expert at all.. I come here looking for advice...but..7 fish at once? Jesus christ thats a lot. How big of a tank? Water specs? etc.etc.

Justin

[exterminator]

Please see the tank specs in my signature bellow.

Water specs are:
Ammonia =0
Nitrite= 0
Nitrate = 0 (strange for a 3 month old tank with some visible waste)
pH = 7.2
KH = 5
GH = 10

Using Aquarium Pharmaceuticals test kit. I'm not sure that it's 100% correct. Ammonia, Nitrites and Nitrates were always 0.

I thought, that adding 7 small fishes wouldn't hurt (4 Kuhliis and 3 Glass Catfish).

[Timmain42]

Check your pH, ammonia and nitrItes again, if you haven't after adding the fish (it reads as tho you have, but it never hurts to double-check). A good-sized (50%) water change may alleviate the problem temporarily, but you need find out exactly what the main issue is.

If you're adding 10 mL of Excel a day, how much are you adding at water change? And since you are using Excel, you can actually get some ripple on the surface for your fish, it won't degass the carbon locked into the Excel (the best reason for using Excel other than tank size).

It's just that 10mL of Excel on a 65G moderately-planted, med-to-high-light tank seems like a lot... on the bottle, that amount is rated for 100G! Your new fish might not be accustomed to that level of chemicals in their water yet, or they might just need more O2. Either way, a temp fix of some surface rippling wouldn't hurt until you know what's going on.

[Kasakato]

Try aiming the spraybar up at the surface to break it up a bit more. I think that you are not geting any nitrates because your plants are using them all, which is ok. Try that for a day and post what you get here.

[exterminator]

I know that adding 10 mL of Excel is a little bit more than recommended, but I was trying to fight building algae. The tank has pretty heavy growth of brown algae on old leaves, gravel and glass.

I do weekly 20% water changes and don't add more than 10 mL of Excel after that. Also add 5 mL of Flourish fertilizer. That's it.

Fish look very healthy during the day. No visible stress. Good appetite.

I'm going to try to redirect the filter output to the surface. This might help.

Do you think my fish load too much for 65 gallon? I used to have more fish in smaller tanks.

[Timmain42]

Seems like a light-to-medium fish load to me. Should be fine, barring other issues.

[exterminator]

Ok. Fish are filling better now. No gasping for the air at the surface.

Redirected the output of canister filter towards the surface as it was suggested here. The tank looks like a river now :)

Checked water parameters again:
Ammonia = 0
Nitrites =0
Nitrates = 0
pH = 7.2
KH = 5
GH = 10

I still don't understand why they didn't have enough oxygen? Plants are growing ok. Well, I never saw them releasing air bubbles though.