Fish Dying, Help Please

[Greenthumbsaz]

My guppies are dying? One at a time. About every third day and only the females?
2 year old, Fifteen gallon tank, 8 adult guppies, just had 25 fry. Also 2 Kory catfish, about 1-1/2 inches long.
My fluval (20gl size) filter gummed up with a milky algea looking stuff and ran dry. I had no choice but to scrub it clean (no soap). I put it back together with a new activated carbon bag and new "bio cubes" in it. I also did a 40% water change and cleaned the plastic plants. I have 3 large very porous volcanic rocks that I would think, harbor a bulk of beneficial bacteria. I never mess with those when cleaning the tank.
2 weeks after the pump cleaning fiasco my ammonia is spiking and 2 big females died. Did 30% change and added "ammo-lock" next one more died. 30% water change every other day, for a week. All tests seem to be stabilizing but I am still losing the females. The strange thing is the fry that are about a month old now are thriving?
On top of that, I have this milky white goo on the glass where an airstone bubbles and it is spreading to the plastic plants. I am not completely new at this but this one has me baffled! Any assistance is WELCOME and appreciated!

 

[N0body Of The Goat]

What are the ammonia and nitrite readings now?
How warm is the water?
What pH is the water?
Have you still got the old bio cubes?
 
On the face of it, this sounds like you have removed a lot of the beneficial bacteria and you are now "fish in cycling."
 
If you have been doing frequent (weekly) water changes under "normal" conditions and of a sizeable volume (~50% or more), you could probably safely change 75-95% of the water without risking "old tank syndrome" killing your fish through sudden major water chemistry changes.
 
When I do my normal ~50% weekly water changes on my 5 active tanks, I often stagger refilling them, initially only adding enough fresh dechlorinated water to get all filters running properly. I then gradually add more buckets over 24-48 hours, thereby reducing the chance of sudden chemistry changes and helping my body cope with all the water carrying!

 

[TheBeginnerAquarist]

I had a similar problem when I was starting my tank. In regular intervals I kept loosing my zebra danios. I would have to agree with N0body Of The Goat that you removed a lot of beneficial bacteria and you are going back to the cycling stage of your tank. I did fish in cycling with my tank and so I would be prepared to see this continue for a little while, but not as long as some people say; my cycle only took only 4 weeks as opposed to 6-8. Also, if you don't already have them, I would recommend getting live plants. They help stabilize nitrogen content and should speed up the process.

 

[Greenthumbsaz]

My ammonia is under .25 / nitrite has dropped to near zero. Nitrates are low as well on the 2nd day after a 50% water change. My ph runs 7.8 consistently and the temperature is 80 degrees. (I live in the Arizona Desert)
I know I lost a lot of the beneficial bacteria in the pump, but with 2 inches of gravel and large porous rocks, I figured it wouldn't be this catastrophic.
Lost my two favorite males today and chemistry is good. Getting ready to do another water change.

Could 4 dime size snails (mystery, I think) be contributing or poisoning the water?

I am giving the big Corey cats away to a friend with a bigger tank. I guess I am going to have to hope the fry make it through this and go from there.
Thank you for the help. I am still listening if anyone has any ideas! Also the milky gooey algea stuff, any ideas?

 

[TheBeginnerAquarist]

I don't think that shrimp could be causing any damage, but I have no experience with shrimp so you'll have to get someone else's input on that.

The milky algae is benign. I had it in my tank too. It will go away eventually. If you scrape the stuff off the glass consistently it should resolve itself. I wish you luck on your tank and if you need any more help I'm happy to help, although I'm definitely not an expert by any means.

Also, I'm not sure what's going on if all the nitrous compounds are low, but that doesn't always mean that you're not still cycling, and that is mostly due to the inaccuracy of testing materials (strips are especially inaccurate).

 

[Greenthumbsaz]

Thanks again, I am testing with a new API master kit. (I wish they used square tubes to make the color easier to match!)
Did another 50% change tonight. The 2 remaining guppies and several 1 month old guppy fry seem to be making progress, will have to wait and see.

 

[N0body Of The Goat]

My ammonia is under .25 / nitrite has dropped to near zero. Nitrates are low as well on the 2nd day after a 50% water change. My ph runs 7.8 consistently and the temperature is 80 degrees. (I live in the Arizona Desert)
 

In my experience, detectable traces of nitrite tend to be more lethal in the short term than ammonia. Nitrite messes with the ability of fish to supply their body with oxygen, a classic sign of nitrite issues is when fish are gasping at the surface (which can also be a sign of simply low oxygen levels, especially in warm water like your 80F).
If I get a positive result for nitrite, a large (>75%) water change is my course of action. If you know what you are doing, you can also add some dissolved salt to the tank, which will lessen the normal effect of nitrite and help your fish breathe.
 
Detectable ammonia levels (for many test kits including API) are more dangerous in warmer and more alkaline water, they are showing you the total ammonia/ammonium level, the equilibrium between these two compounds changes with temp and pH.

 

[Greenthumbsaz]

If I get a positive result for nitrite, a large (>75%) water change is my course of action. If you know what you are doing, you can also add some dissolved salt to the tank, which will lessen the normal effect of nitrite and help your fish breathe.

I have salinity testing equipment at work. What are the parameters? I would guess the "Aquarium salt" not Marine salt would be the choice? Your input and recommendations are appreciated.

As a professional Horticulturist for 30years, I have learned the fighting with Mother Nature is a losing battle in the long term! I now try to find a way to help nature take its course more quickly to reach a positive outcome. The trick is knowing how to nudge nature away from the negative path. This is why this tank cycle is bugging me so much. My results so far have been marginal at best, so I will keep learning.