Sometimes I Feel Like I Can't Win


Resurrecting the Passion of Fishkeeping
Nov 12, 2009
Reaction score
Ok - background.

72 gallon bow. low tech planted (no C02/ferts/anything), predrilled with overflow/filter housing. Filtered by two Fluval 405s with outtakes housed inside the filterhousing to reduce flow for discus. One filter is 3+ years old and the other is under a year old.

I had been running the tank about 1- 1.5 inches lower than the top of the tank so there would be a tiny cascade/waterfall between the filter housing walls. It made a sort of bubble curtain in the back of my tank. But it also made noise. The other night (Sat) Hubby was not feeling well and wanted to lay out on the couch watching tv when I went to bed, so he asked me to stop the bubbling noise in case he drifted off. It was late and I was exhausted, so I just topped off the tank with a little under 3 gallons so the water level was high enough so the water flowed straight out instead of down.

Once the tank was full and silent I noticed one of my filters was making more noise than the other. It doesn't sound exactly like grinding, just an intensified hum. I assume it had been doing that for a while, but over the sound of the "waterfall" in the tank it went unnoticed.

It was too late to start tearing it apart, so I unplugged it to keep the motor from burning out and went to bed.

I woke up early the next morning (Sunday/yesterday), turned the filter on to see if the noise had stopped and a whole load of crud spewed into the tank. And it was still noisy.

I disassembled the filter while doing a water change. I cleaned out the housing and the propeller area (Kept the media wet and rinsed off in a bucket of tank water), but after filling the tank up after about a 75% water change due to the extra crud pushed into the tank.

I filled it back up, and started up just the working filter. The way the water flows out the top of the housing causes a gentle ripping across the surface of the tank. For the rest of the day all seemed well and I just resolved to buying a new motor housing for the filter next week once I got my bonus check.

Woke up this morning (Monday) and all the fish are breathing at the surface, a few discus have darkened and I had lost 3 baby angelfish and a female threadfin rainbow. (Possibly my young albino bristlenose plec but I realized I have not seen him for over a week or so and I can't find him or his remains anywhere)
Fish stock now stands at 7 discus (still young, most around 4.5" or 3.5:", two at just under 3"), 4 threadfins (will try and bump the numbers up again once tank is resolved), 5 sparkling gouramis, 6 sterbai corydoras, 1 betta, 1 quarter size angel, 1 nickel size angel and 6 just around dime sized angelfish. (added them here to see the difference between tanks/temp and growth rate.

The betta and sparkling gouramis are acting fine and the sparkling gouramis are even clicking and displaying at each other as they do every day.

I added an airstone and with in an hour most of the fish are back to swimming about normally. My paramaters are Ammonia 0, Nitrite 0 and Nitrate barely registering. 84*F.

Did I have a tiny spike during the night due to being down 1/2 the filtration and the remaining filter caught up by the time I woke up? Are the fish now used to the increased oxygen caused by the waterfall and that change suffocated them? Do I have to keep the airstone in longterm or...?


Reef Tank, Crustacean, and Puffer Enthusiast
Staff member
Aug 20, 2012
Reaction score
gourami and betta do well in lower oxygen environments but most other fish require some kind of surface aggitation to promote gas exchange that keep the water well oxygenated. If the airstone is the only way you are doing this then it does need to stay but there are other ways you can use as well. You already mentioned how the waterfall did this.
Just based on the above low oxygen is my guess but why it was low can be a combination of things.


New Member
Dec 11, 2011
Reaction score
Sorry to read your misfortune.
do you have access to a dissolved oxygen test kit? you would need to take a reading just before the lights of the tank on (before photosynthesis begins) and one later on.
When the lights switch off plants absorb oxygen and release CO2. It is possible that overnight , with the reduced water surface agitation your plants and the fish depleted the available oxygen in the water.
I guess that you either need to revert to your older setup with the waterfall or keep the airstones running

Most reactions