Personally if it was my tank, I would not be concerned about pH swings of 0.3 throughout the day.

I'm certain people running DIY CO2 will experience even larger swings as the output rate is inconsistent, and it's left running at night when CO2 is going to accumulate.

Do the fish seem to be having any problems? Are they healthy?

I know my tank fluctuates over 24 hours because I don't have a pH meter on my CO2.

The reading I've done into it has led me to the opinion that small regular fluctuations are fine, as long as they aren't happening suddenly.

 

I've had a few problems--somewhat high mortality with my white clouds (not all the crayfishes' fault) and now some bug is going around that is making the fish flash. I had an "incident' a couple weeks ago with a stick that was decaying that I had to take out, that's when the flashing started, but only with one of the guppies. Whatever he had has spread since then. I think it may just be a matter of the disease getting a foothold and becoming too much for the fishes' immune systems to fight off, but I thought maybe these daily pH swings over the past week were adding to their stress level and making them more susceptible to the infection.

Right now the plan is to put them in a temp tank and treat them with coppersafe, but I want to eliminate any additional stressors that might be in the tank.

 

From what I can remember in Diana's book, pH fluctuations like what you are dealing with are very normal in both aquariums and in nature because there is more CO2 in the water at nighttime or when the lights are out compared to during the day when there is more oxygen.

I've noticed it with my own tanks. I had tested my 20g just before the lights turned on in the morning and the pH was around 7.8 yet at the end of the day when the lights went out, it was up to 8.2 and everyone was fine because it was gradual. My water is also hard as well(the GH is around 28dGH and the KH is around 8-10dKH).

I think the tanks may be overstocked. That's the first thing that came to mind when I read what you have in both tanks but I also don't like to overstock my tanks so I could be wrong. Also, flashing is not only caused by disease. Ammonia and nitrites in the tank can also cause fish to flash so there may be some in the tank.

I am interested in the ammonia test kit you are using. Do the colors on the chart go from yellow to green or is it more amber shades? If you are using a test kit that changes to the amber colors then you may want to get the one that goes from yellow to green. I've found that the amber ones are sometimes affected by certain dechlorinators whereas the yellow/green ones aren't affected by such things and they tend to be more accurate from my experiences.

Did you test the tank for nitrites? I'd say that testing for both ammonia and nitrites is far more important then testing for nitrates. Nitrites can do just as much damage as ammonia so testing for it is a must.

 

Ph movements like that are very normal. Especially in a tank with organisms that photosynthesize. Dont be alarmed and dont try and "correct" it with chemicals. As long as the Ph doesnt move quickly there will be no stress to your livestock. They are used to a natural Day/night Ph swing.

 

Mandy and others, thanks for the feedback and suggestions!

EDIT: Sure enough, nitrites in the quarantine tank were around 3ppm. That couldn't be because of a mini-cycle if the tank was only running for a day and a half, could it? I detect no ammonia. It's possible it was something else, like the old substrate that was in the tank, which I washed, but still... I tried one of the strips on the same water for comparison and it *barely* registers nitrites--it looks like .5ppm, definitely not 3. So the strips were faulty. (I wonder why this is so common? My friend just had a problem with a liquid pH test a few weeks ago, it was telling him his water was 7.4+ when it was actually around 6.)

More water changes are in my future...
end EDIT.

re nitrites, I used 5-in-1 strip tests before and never got any nitrites, but I'm not sure if I tested with the strips after I got the liquid test kit, so I'll check with that.

re the ammonia test, mine is the kind that goes from yellow (0 ammonia) to green. The yellow on the chart is a kind of golden, warmer (almost orange) shade of yellow, but when I test tapwater or my aquarium water they both come up more of a pale, medium yellow. When I only tested the tank water I thought it meant I had a tiny bit of ammonia, but then I compared side-by-side with tapwater and I couldn't tell any difference, so I'm thinking that's how it looks with 0 ammonia.

I try to age my water for water changes instead of adding a conditioner, since Chicago tapwater is pretty high quality and has relatively low (.7 ppm) chlorine, and doesn't use chloramines, and I thought, why spend money and add extra chemicals to the tank? (I do have a bottle of conditioner on hand though.)

The reason I thought the flashing must be from disease is the way it spread from one fish to the others, and the way it comes and goes. The first fish (a guppy) that had it recovered after maybe a week. Then a white cloud started flashing, then days later another 2 white clouds started and the same guppy started up again. The first white cloud died around that time. Now, since I put them in the QT, it's hard to look because I keep a blanket over the tank, but it looks like the other guppy is flashing, and the first one has stopped, and the clouds may have stopped.

I found out white clouds don't tolerate copper, so I'm keeping it dark and added about 1.5 teaspoons per gallon salt--this was the suggestion of an employee at a local (and very good) LFS. He said velvet is pretty rare nowadays, so I am just trying to make them comfy and boost their immune systems as much as anything else. I suppose I should change a lot of the water in that tank (it was mostly from the original tank--I wanted to avoid shocking the fish) now, in case it's something that was in the water?

 

Nitrites are a pain! I've struggled with them in the past and take it from me, it takes less time to drop the ammonia down to zero then it is to get rid of nitrites. Also, you may want to stick with drop test kits. They are more accurate and I've heard stories of people saying that the test strips tend to be off so drop test kits are the best way to go.

The mini-cycle could have very well caused the nitrites. Those things can show up when you least expect them. Here's a little story about what happened to me. When I had a 10 gallon guppy tank, I noticed everyone was acting strangely so when I tested the water, the ammonia was fine but the nitrites were in between 0.25-0.50ppm! The tank was well over a year old so I didn't know why they would show up now. I did water changes for a few days but nothing worked. The cause of them was from the sponge filter in the tank. I had slacked off in cleaning the sponge so the debris that accumulated caused a spike in nitrites. I thoroughly cleaned the sponge and in 24 hours, the nitrites were gone!

As for the ammonia, the test results sound fine. When I test my water, the yellow looks almost like a very bright yellow. Now when the yellow has a green tint to it then that's a good indication of a trace amount of ammonia.

Aging tap water will only remove any chlorine that's in there. It will not remove/neutralize heavy metals so your fish could very well be reacting to that. I know it may seem like a pain but it's worth it to treat the water prior to putting it in your tank whether it be a new tank set up or water changes. If you want a conditioner that lasts I recommend Seachem Prime. 1ml will treat 10 gallons of water so it will last quite a bit. I have one gallon jugs sitting out for in case I need to change some water and I only have to add two drops to each gallon. The conditioner won't hurt any in the tank and many people strongly recommend it even for people who use well water because of the heavy metals.

I'll admit that I have no experience with cloud minnows but I do have some for guppies and what I've noticed with them(I'm assuming you have males) is that male guppies will sometimes flash as a way of marking their territory, so to speak. I've seen it many times with my little ones. If I put a new guppy in there, they will flash off of the gravel and plants for a couple of days and then they stop. Your little ones could have been doing that. Does your cloud minnow have a goldish dusting on them like this? That's what Velvet looks like.

If you had used all new water, you would not have to worry about shocking the fish if you acclimate them to the new water. I've done it before with no problems. When I acclimate new fish, for example, I gradually get them use to the new water for about an hour and then I put them into the tank whether it be a QT or the main tank. It know that sounds like a long time but it's worth it.

 

That's interesting about your filtration failure leading to a nitrite spike, rather than ammonia.

I don't trust my eyes because the fish are all so small, and all of them are pale yellowish or pale olive green, so it's hard to tell that color from what the velvet is supposed to look like. The one white cloud that died looked like it had a lot of extra slime. But, that said, I can't see any velvet. I definitely don't see sugar grain-sized spots, so I don't think it could be ich.

Lots of water changes and upped the salt dosage to about 3 tspns/gallon, waiting to see how they respond...

 

When I mentioned the Velvet I knew I was forgetting something. I forgot to say that to get a good look for Velvet, you need to use a flashlight(not the LED ones) and a magnifying glass. You will be able to see any dustings far better that way then with just your eyes.

The slime buildup on the minnow that died could be from anything. I still think that perhaps heavy metals could be to blame if you are just aging water and not treating it with anything.

 

Ah, that helps! So I did this with a few fish, a white cloud and some juvenile guppies (one of them flashed this morning, the only time any of the fish have flashed today that I've seen). The only gold or green shiny spots I see look like they must be part of the fish's natural coloring, they are in precise, symmetrical patterns in particular areas (stripes along the side, around the gills, concentrated around the dorsal fin, on top of the head between the eyes). Not patchy like I would expect an infection to be. In the picture it looks like the velvet spots are between the fish's scales, but I didn't see anything like that.

Why do you say not to use an LED flashlight? I used my bike headlight. It's very bright, but it might use an LED lamp--or maybe halogen, I'm not sure.

The fish are acting very normal (perky, feisty) today after another water change. If it turns out they didn't have velvet, I'm thinking I should just release them into the old tank again soon.

 

Resolution (sort of): I think it was mostly how high the pH got at the high end of the daily pH swing that was the main cause of the problem, not the amount of the swing or other factors such as contaminants. The white clouds, which are less tolerant of alkalinity, seemed to have by far more problems than the guppies.

To make a long story short, the flashing was much less or not noticeable at all when the pH was lower (early morning especially), but would get bad in the afternoon and/or when the pH registered 8.1 or more. And that was the case in the QT tank too. I don't think there were any nitrites in the main tank, I think they were from the insufficiently-washed substrate in the QT tank.

I think there were other factors involved too, since the pH gets almost as high (at least up to 8.1) in the 5-gallon tank and none of the guppies in there have been flashing, and the 4 otos seem okay, and there has been no mortality anytime recently.

I had a concrete decoration in the main tank which I took out a few days ago, and changed a lot of the water, and this afternoon the pH high was 7.8. Although it was overcast, so that might have made a difference, but probably not a large one, since the pH usually plateaus by quite early in the afternoon. The fish are back in the main tank and acting pretty normal (lots of courtship displays). Worst case scenario is that the rise in alkalinity was mainly from the substrate (which has a bit of shell matter), and I will have to partially tear down the main tank and remove most of the sand layer of the substrate, but I'm actually not *too* worried about this, since the pH was pretty stable before adding that last piece of concrete.

I will treat any added water in the future with water conditioner...chelate those metals!

Thanks tons for the advice! It was very helpful.