Snails and plants thriving but fish dying?

[NoLa24]

I'm at my wits end. I started up a 30 gallon freshwater tank a few months ago. Took several weeks to cycle with live plants in it. Finally was testing at 0 ammonia, 0 nitrates, and 0-5 nitrites consistently. Added 6 fancy guppies, two weeks later 6 dwarf rainbow fish, and two weeks after that 6 yoyo loaches.

All was well for a few weeks, went to do a water change, water tested fine before hand, changed ten gallons (as per usual once a week), a day later over the course of a few hrs 5 rainbow fish and 3 guppies died. I quickly transferred the remaining fish to my 20 gallon tank and with the exception of the lone rainbow that died a couple hrs later, all original 3 guppies and 6 yoyos are doing fine.

I did some research, and found out about sand causing gas bubbles if not stirred. I have sand in both tanks, however the 20 gallon gas pretty much always had trumpet snails, so I didn't even know stirring the sand was a thing and I do remember seeing quite a few bubbles come up when I added the water and disturbed a section of sand. I took some trumpets and put them into the 30 gallon. Now here's where things get odd.

For the next month or so the plants all showed substantial growth, and the trumpets have absolutely thrived. I mean they have never gotten nearly as big in the 20 gallon despite breeding without issue. So once I was sure the snails were well established I tried adding in three guppies. Next morning two were dead so I put the alive one back with the others.

I will note that I bought 4 additional guppies the day before, but then realized I had miscalculated the male to female ratio which was part of the reason I put 3 males in the 30 gallon. The two that died were from the new ones, and a couple days later the other two died, the original ones are all still fine. Is it possible they were just not good stock? I did get them from a different store then I usually go to.

Did some more research and the only thing I found that I thought pertained was it said that if your light is too bright it can cause rapid ph swings. My light was set at a bright setting because the tank is tall, so I have since turned it down. But my question is if that was the cause, wouldn't the snails not be doing as well as they are? And yes, before you ask, I've been testing the water frequently and everything tests perfect.0/0/0-5 (ph 7.4-7.6)

 

[Uberhoust]

I don't know if I can help but I can address some things.

• Assuming 1-5 nitrate and 0 nitrite. If it is 0 nitrate and 0-5 nitrite you have a problem with your cycle, and the nitrite could be killing the fish
• I wouldn't stress about a 7.4 to 7.6 pH swing
• I have sand in both of my current tanks, they have been running with this substrate in the 37 gallon tank now for 2.5 years and I haven't had and hydrogen sulfide produced yet. Do you have anything under your sand? I doubt this is the issue.

The deaths seemed to be when you change things over either adding new fish or changing the water. Is your water treated and are you countering that when you do your water changes, I expect you are. Is there something about the tank that might be wrong, a partially failed heater that leaks electricity into the tank, I have had this happen once.

Other things to look at, what are the fishes behavior before they die, what do they look like when they are dead. It seems like they die pretty quick. Do the snails stay in the sand, have any of them died? Do you have any unusual plants in your tank? perhaps a normally terrestrial plant that is poisonous to fish but not mollusks.

 

[NoLa24]

I don't know if I can help but I can address some things.

• Assuming 1-5 nitrate and 0 nitrite. If it is 0 nitrate and 0-5 nitrite you have a problem with your cycle, and the nitrite could be killing the fish
• I wouldn't stress about a 7.4 to 7.6 pH swing
• I have sand in both of my current tanks, they have been running with this substrate in the 37 gallon tank now for 2.5 years and I haven't had and hydrogen sulfide produced yet. Do you have anything under your sand? I doubt this is the issue.

The deaths seemed to be when you change things over either adding new fish or changing the water. Is your water treated and are you countering that when you do your water changes, I expect you are. Is there something about the tank that might be wrong, a partially failed heater that leaks electricity into the tank, I have had this happen once.

Other things to look at, what are the fishes behavior before they die, what do they look like when they are dead. It seems like they die pretty quick. Do the snails stay in the sand, have any of them died? Do you have any unusual plants in your tank? perhaps a normally terrestrial plant that is poisonous to fish but not mollusks.

Yes sorry I typed the nitrate/nitrite in reverse. As far as the ph those are just the reading when I test the water every few days. If I understood what I read earlier, it sounded like too bright of light could cause rapid ph swings throughout the day. I thought about it some more and realized that the fish that have died quickly when placed in the tank, seemed fine during the day/were active but when i looked at them in the morning they were dead and appeared to have been for several hours.

The heater is brand new but I will check it tonight. Everytime I check the temp it's always right around 79-81°.

All the plants are very basic ones like swords and annubis and such. In addition to the trumpet snails that are actively moving around and breeding as well as growing, I also have two nitrate snails that are very active as well. I did have one die, although I had had it for awhile now so I assumed it was just old.

I treat the tap water with dechlorinator and make sure it's a similar temp when doing water changes. The only difference between this tanks sand and my 20 gallon and 5 gallon established tanks sand is I used pool filter sand instead of aquarium sand. However I rinsed it VERY thoroughly.

 

[Uberhoust]

Seems like everything is right, nothing wrong with pool filter sand, other than it can be real bright. Have you tried with less intense lighting yet? I still don't think that would be the issue but I have been wrong before.

Is it the pool filter sand in the aquarium that is having an issue?

I really don't know what else to suggest. I don't see how hard your water is, but even if that is wrong it wouldn't kill the fish as fast as you say. I have had dwarf rainbow in the past and one thing about them is that they like to have secure and open areas, to hide and swim, they can be a bit of a nervous fish, but again I cannot see them dying within a couple of days.

Perhaps we need to look at all the aspects of the tank, from your original post

All was well for a few weeks, went to do a water change, water tested fine before hand, changed ten gallons (as per usual once a week), a day later over the course of a few hrs 5 rainbow fish and 3 guppies died. I quickly transferred the remaining fish to my 20 gallon tank and with the exception of the lone rainbow that died a couple hrs later, all original 3 guppies and 6 yoyos are doing fine.

This strongly suggests something was introduced into the water at this time. Is it possible you missed a water treatment, I have done that in the past, and noted the fish in distress soon after a water change, then quickly added the treatment. Perhaps the water supplier upped the chlorine, or changed to Chloramine instead of chlorine. This likely does not explain the second loss of guppies.

 

[Slaphppy7]

What kind of test kit do you use? What type of water conditioner?

When performing WC's, are you using buckets or a hose? Are you matching the tap temp to the tank temp as closely as possible when performing WC's?

 

[Byron]

The first thing we need to know is the GH and pH of the source water (tap) on its own, and of the tank water. Numbers please so we can be certain.

Second, while some of the identified issues could weaken certain fish, things like light, pH, sand bubbles are not likely to kill them this rapidly. Bright light can be extremely stressful though, and this can lead to other issues that would seem totally unrelated.

Third, there could be an issue with the selection of fish species. The GH and pH will help here, but have you sat without moving in front of the tank for some time to see how the fish react when they forget you are there? This is not silly...fish see you and it registers as likely food, and their interactive behaviours can be very, very different once they forget your presence. Where I am going at here, is the loaches; this species (Botia almorhae) are known to fin nip upper fish, and even the intent of the loaches to do this will cause severe stress to the upper fish that can read the allomones (chemical signals) the loaches are communicating.