Rosy Red minnows dying, water chemistry seems ok

[MadDave]

Hello, all. I'm hoping to tap into the collective wisdom of folks here.

I've got a relatively new pond (6 months) of about 2500 gallon capacity, 3.5 ft deep, and have recently started adding fauna to it. The pond is fed by an artificial stream driven by a 2500 gal/hr pump, and has about 120 gals of bioball filtration in addition to a lot of rock and gravel filter in the water flow.

I started with 100 rosy red minnows, who seemed pretty happy in the pond for their first week. I also added 25 crayfish at the same time. Things seemed stable, and a few of the rosies were even trying to breed.

About a week later, I added 100 trapdoor snails to help manage the algae. I realize this is adding a lot in a short period, but the size of the pond has kept me comfortable about it, and the water chemistry hasn't looked at all worrying.

The very next morning, I had 3 dead minnows, and a few more die every day. There were 9 dead ones this morning, bringing the total to about 25. My resident newt has also disappeared.

The water chemistry looks pretty good:

• pH 7.6 (was 8.4, then I added some peat moss),
• no detectable ammonia, chlorine, nitrites, or nitrates
• the GH is around 30 (pretty soft, I know - the pond is replenished with captured rain water).

Air temp has been cold at night, getting down to ~34 F, but around 50-70 F in the afternoons. Their ability to handle winter temps is why I got the rosies.

Any ideas? The correlation to when I added the snails is interesting, but it seems too fast (12 hours) for them to be the cause of the first deaths.

 

[WaterGardener]

What is the KH?

8.4 is not a problem for the pH.

Rain water can be very acidic and can cause your pH to fall. Have you tested the pH of the rain water?

 

[MadDave]

KH is at about 70.

No, I haven't tested the rainwater's pH, but I'm on the west coast of North America, and climaten data says our rain runs around 4.6. Given the high pH of the pond, though, I'm not thinking it's getting too acidic for the fish.

 

[WaterGardener]

It may not be too high, but it may be fluctuating whenever you add rain water. That alone can kill fish.

The KH is a bit low. I like to see it at least 100, even much higher.

 

[j.w]

@MadDave

 

[MadDave]

The KH is a bit low. I like to see it at least 100, even much higher.

I'm increasing it over several days, will aim for 100-125.

I'm also dosing the pond with Melafix daily; it was suggested by my fish store, and aligns with what I remember from the days when I had 11 active tanks in my basement.

The progression puzzles me; between 3 and 9 dead every day is not a pattern I'd expect from ammonia, nitrites, or nitrates. AND, the steady pace isn't what I'd expect from a contagious pathogen (I'd expect a more exponential increase).

This is the pond. the river rock (large, round gravel for those parts of the world that don't call it that) is 1 layer deep in the deep section. There's about 4" of it over the bio filter and pump (the area on the right). The pump is around 2500 gal/hour.

 

[addy1]

Welcome to the forum!

Nice looking pond!

 

[GBBUDD]

pH 7.6 (was 8.4, then I added some peat moss

maybe i am missing something but peatmoss is the basic to an acidic side of the ph scale if your low why would you add peat. this will lower your ph. Adding baking soda will help increase your ph and kh. but do so slowly one cup will raise your ph per 1000 gallons by 10 points on the kh scale

 

[GBBUDD]

You have a new pond and it takes time for the bacteria to become viable enough to protect life in our ponds. 6 months old does not mean the pond has reached this point. adding 100 of everything at one time in a new pond can create an ammonia spike particularly if you loose a few due to not acclimating properly. a poor acclimating can be the reason the fish die within a few days.

 

[WaterGardener]

The picture you posted makes it look as though runoff from the area surrounding the pond can flow into the water. Is that the case?

 

[MadDave]

The picture you posted makes it look as though runoff from the area surrounding the pond can flow into the water. Is that the case?

No, the elevations are such that runoff goes around the pond; we were thoughtful about that. I agree the picture suggests that.

 

[MadDave]

maybe i am missing something but peatmoss is the basic to an acidic side of the ph scale if your low why would you add peat. this will lower your ph. Adding baking soda will help increase your ph and kh. but do so slowly one cup will raise your ph per 1000 gallons by 10 points on the kh scale

The pH was 8.4. The internet (which knows everything) says rosies prefer 7-8, so I added the peat moss to drop the pH, which it did.

 

[GBBUDD]

It may not be too high, but it may be fluctuating whenever you add rain water. That alone can kill fish.

The KH is a bit low. I like to see it at least 100, even much higher.

PH is generaly not as important as is stability " within reason" quick jumps up and down kill more than does high or low ph

 

[MadDave]

Update:

We're down to about 7 (from 100) visible survivors, but haven't lost any over the last 3 days, and the survivors are (so far) acting normally.

7 days of Melafix and 4 days (so far) of Pimafix may have done the trick.

 

[GBBUDD]

many types of fish will not do well in a medicated tank