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post #1 of 9 (permalink) Old 01-19-2006, 05:44 PM Thread Starter
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Fish Kill (long)

I am trying to figure out how I killed 4 discus and I think there could be several things going on. I hope someone can help me sort it out.

Last weekend I made a rookie mistake. My filtration consists of a Fluval 403 that is usually cleaned every blue moon and a Magnum 350 with the micron filter that injects the CO2. I know the Magnum doesn’t provide biological filtration so I clean it almost every week. I have been doing this for 9 years (2 years with CO2). I started to think that maybe my algae problem had something to do with the Fluval being dirty. I had added the discus in November increasing the fish load so I cleaned it on Saturday at the same time I did the Magnum. Even though I only cleaned half of the sponges I woke up the next day to find the discus really stressed. One was dead and several of the others were lying on their sides at the bottom of the tank. All water parameters tested normal except for the nitrite test which gave a reading of 0.3 when I normally don’t have anything, so I figured that was the problem. Two 50% water changes got it down and the rest of the fish recovered. This was on Sunday.

Monday and Tuesday nitrites were 0 and things in the tank were back to normal. Tuesday evening I did a 50% water change. I didn't look at the tank closely Wednesday morning and got a call from my wife that another discus had died. She said all the fish in the tank were gasping at the surface. I got her to get that fish out of the tank, and she told me later in the day that everything seemed OK in that they weren't at the surface any more. (Realize she is a non-fish person.)

When I got home I found there were 2 more dead discus in the tank. Judging by their condition I think they were gone for a while, but my wife didn't see them in the plants. I ran tests and again nitrites were the only bad reading.

Tank stats:
150g, torn down in October and restarted, heavily planted
240W for 3 hours, 560W for 3 hours, 240W for 3 hours
Pressurized CO2
100% Flourite
PH 6.4
KH 5.5
GH 9
Nitrates 10
PO4 – 2
No ammonia
Temp 85

Weekly EI Dosing:
1 t K2SO4 3x
1/4 t KH2PO4 3x
2t MGSO4 3x
60ml CSM+B on alternate days (1Tbs in 500ml solution)
50ml Excel daily (for the past 9 days)

I do 50% water changes twice a week. My source is well water with PH of 6.6 that out-gasses to 7.2. KH is 3.5 so I add baking soda to take it up to 5.5. (This is a recent change – I had been raising it to 4.5.)

I hooked up an airstone to run after lights out last night in case O2 or CO2 was the problem and this morning nitrites were 0 again. Everything else was normal and fish seem happy.

These seem to be the possible causes:

>Cleaned the biofilter too much.
>Water change left a low O2 concentration in the tank.
>Dying algae due to Excel treatment spiked nitrites.
>Reaction to the Excel treatment itself.
>PH swing due to adding baking soda for KH stressed fish.

The problem is none make sense for both nitrite spikes since I didn’t have a problem for 2 days in the middle. I really doubt the low O2 theory because when I do the water changes I get good pearling.

Any thoughts?
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post #2 of 9 (permalink) Old 01-19-2006, 08:47 PM
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Quote:
Originally Posted by zelmo
>Cleaned the biofilter too much.
Quite possibly. I'm guessing you cleaned it to close to pristine, which removed a lot of the biofiltration bacteria. I'm also guessing you cleaned the 1st sponge after the filter intake, which has the majority of the bacteria.

I'm hoping you did not rinse it under tapwater - the chlorine will harm the bacteria. The safest way is to get a container of tank water, and clean the filter in that as to not shock the bacteria.

Quote:
Originally Posted by zelmo
>Water change left a low O2 concentration in the tank.
Possibly, if you did the water change before lights-out, and you don't aerate your tank during that period.

Quote:
Originally Posted by zelmo
>Dying algae due to Excel treatment spiked nitrites.
I don't think dying algae releases nitrites. Nitrates are more likely.

Quote:
Originally Posted by zelmo
>Reaction to the Excel treatment itself.
If you're overdosing Excel to treat the algae, it can stress the biofilter.

Quote:
Originally Posted by zelmo
>PH swing due to adding baking soda for KH stressed fish.
pH swings aren't too harmful (but KH swings are). Of course, if you did it before lights-out, and CO2 injection is off during that time, it would have prolonged the pH swing. And since you have so many other stressors in the tank, that might have contributed, even if it wouldn't have been enough by itself.
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post #3 of 9 (permalink) Old 01-20-2006, 12:58 AM Thread Starter
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Thanks, DC.

Just a couple of remarks.

>If the plants pearl after the water change, doesn't that indicate O2 saturation?

>I'm on well water. There is no chlorine.

>I never heard Excel could stress the biofilter. Are you confusing that with Maracyn?

What I am finding strange is that the nitrites were down for 2 days and went up after the water change. (Tap tested 0 nitrites.) Could the dead fish in the tank cause that? If so, I guess its possible the first kill was due to the biofilter being depleted, and the second kill was due to changing the KH (and by proxy the PH) with the lights going out shortly after.
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post #4 of 9 (permalink) Old 01-20-2006, 02:15 AM
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I though I would throw the well water situation out there.

It seems to me that there could be variety in the quality of this water.

Could there have been any flooding, some type of discharge locally or something that affected the source water quality? I am assuming you do not test your source water every water change, and 50 percent twice a week could introduce a lot of a contaminant if it happen to be in the water.

Just a thought.
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post #5 of 9 (permalink) Old 01-20-2006, 04:45 AM
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Quote:
Originally Posted by zelmo
>If the plants pearl after the water change, doesn't that indicate O2 saturation?
The heavy pearling seen after a water change is just dissolved gasses in the new water coming out of solution, and should not be confused with the pearling of pure O2 as a result of photosynthesis. There was some discussion on that recently when someone reported their fish were pearling after a water change.

Quote:
Originally Posted by zelmo
>I'm on well water. There is no chlorine.
Oops, I missed that.

Quote:
Originally Posted by zelmo
>I never heard Excel could stress the biofilter. Are you confusing that with Maracyn?
No confusion. The active ingredient in Excel is gluteraldehyde, which is related to formaldehyde. It's a broad spectrum biocide, and at sufficient concentration it will kill everything in the tank. But the dose makes the poison. At normal doses, it's harmless. If you overdose to treat algae, you're using concentrations high enough for it to be toxic to lower lifeforms. Fortunately the biofilter is resilient, but not immune - especially if it has been pre-stressed by other factors. I have seen reports of people knocking out their biofilters with accidental overdoses.

I don't know exactly what happened in your tank, all I can offer is some possibilities. It sounds like there were several contributing factors that added up.
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post #6 of 9 (permalink) Old 01-20-2006, 01:58 PM Thread Starter
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Thanks for clearing up the pearling issue. I missed the post where fish were pearling; I'll look for that.

Quote:
Originally Posted by DarkCobra
It sounds like there were several contributing factors that added up.
That is what I think also. But I am also leaning towards the KH change due to adding baking soda as being the one that pushed it over the top. The drop in nitrites that I got after the emergency water changes seems to indicate the biofilter did recover and that I screwed it up again during the second water change.

Quote:
Originally Posted by putty
Could there have been any flooding, some type of discharge locally or something that affected the source water quality? I am assuming you do not test your source water every water change, and 50 percent twice a week could introduce a lot of a contaminant if it happen to be in the water.
There hasn't been anything going on that would change water quality. There was a time when I never tested the well water, but I have been doing that on a regular basis lately. I did not test it before the WC that killed the first fish, but I did test it before the emergency changes and the WC that preceded the second kill. Since the fish recovered after the emergency changes I don't think there is something in the water my kits are not picking up.

Do you know if having the dead fish in the tank would give me the nitrite reading?
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post #7 of 9 (permalink) Old 01-20-2006, 02:53 PM
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Sounds like my discus deaths

50% water change with well water, CO2 injection... gasping fish, dead fish.

I vote for low O2 water combined with high CO2 from well water plus CO2 injection for high CO2 rates that make low O2 even more dangerous.
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post #8 of 9 (permalink) Old 01-20-2006, 04:24 PM
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Dead fish can cause an enormous spike in nitrites and nitrates, but only if you leave them to decompose in the tank. Imagine dumping an equivalent portion of food in the tank. If you got them out within a few hours they probably didn't contribute.
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post #9 of 9 (permalink) Old 01-20-2006, 05:00 PM Thread Starter
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If you got them out within a few hours they probably didn't contribute.
I really don't know how long they were in the tank. I noticed the first one at 8 AM. I could have died at any point during the night.

The second time could have been even worse. One fish was removed around 10 AM, the others were removed at 6 PM. Since I don't know when they died I don't know how long they were in the tank. It could have been 12 hours or more.
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