My pH has been climbing during the day while the tank light is on, but dropping at night while the light is off. My alkalinity had been high, holding up my pH, but after a 50% water change, I've had moderate (80 ppm) alkalinity. My pH continues to fluctuate.

Just wondering if this was something related to the light. My other levels are great, but I can't keep pH stable. I now have ick being treated, which I'm guessing is due to the pH fluctuating so dramatically for two days. I lost my pleco I hope my others make it.

How much fluctuation are you getting? Some aquarists believe that pH fluctuations are not as stressful on fish as previously thought.

Do you have any live plants in your tank? I know they can affect pH at night when they use oxygen for respiration and give off CO2 which converts to an acidic form driving down pH. Then during the day as they use CO2 for photosynthesis, that takes away some of that acidity and the pH is driven up.

A KH of 80 ppm is the lowest most people recommend to buffer any acids your fish are introducing via waste products. Unless your tank is drastically overstocked, it seems unlikely that enough acid is being introduced. What is the stocking level in your tank? (How many fish?)

Try adding baking soda to bring up your KH and hopefully give you some stabilization on your pH. Take a glass of your tank water and stir in the baking soda, then add that to the tank. Don't use much a teaspoon at most for ten gallons

It's going back and forth between 7.4 and 8.4.

I do have a live plant and that's really cool to know.

I have two fantail goldfish, 5 gallon tank.

The reason I was concerned was because I think it caused them to get ick and I didn't know whether I should leave the light off or on permanently to remedy the issue and prevent a relapse.

Would the baking soda be idea during ick, or a bad one?

With that kind of change you are looking at a tenfold increase and/or decrease in acidity.

Its hard to believe that would not be stressful to a fish.

Like i said before some aquarists believe that ph changes aren't that stressful to fish but I would disagree. You also have to consider that ammonia is much more toxic at ph's above 8 than it is at ph's around seven. (that is probably why some people consider ph fluctuations "stressful") So the combination of ph fluctuation stress and ammonia stress have probably made your goldies susceptible to ick.

I have never treated ick but have battled other diseases. The baking soda will not hurt or help in treating the ick but it will help to stabilize the ph. and that is always beneficial for the fish.

With such a small water column fluctuations can happen very quickly. I would do a water change (not much maybe a gallon at most), add your ick medicine, stir a half teaspoon of baking soda into the water your gonna put back in the tank, and fill the tank back up. this should roughly double your KH readings.

Treating illness is a tough task...as soon as you think its gone do a 50% water change (add some baking soda to the new water ) and fill it back up. Don't worry about overdosing the baking soda. I have had goldfish in 25 degree KH (450ppm) water and saw no ill effects. The only downfall of having a really high KH is that the pH will stay fairly high (When i had my 450ppm KH water i couldnt get the ph below 8 no matter what i tried) thus ammonia will be more toxic so weekly water changes become important.

STABILITY is more important than a targeted pH. (but i think you know this already )

Do you know what kind of plant you have in your tank?

You know, I honestly couldn't tell you what kind of plant it is. I know it's not a water lilly, any type of grass, or mint charlie. I've had all those previously and this is something different. I prefer the grass or mint charlie, because it's dense and they can hide and rest in it. The plant I have now is two long sprigs with a leaf a piece. It's not very appealing, but it hasn't died, so I've kept it. Everything else died in my previous tank.

Thanks for the advice, I guess it's up to me whether to leave the light on or not, because if it's causing the fluctuation, it's going to continue causing a problem. All my other levels are good, amonia has stayed low, so... I'll just leave the light on and buy a shady plant they can hide in.

Good luck !!!

If you have any more questions please ask.

Kevin

I just read a forum about leaving lights on 24 hours a day. Apparently the persons timer had messed up and started turning all his plants yellow. But the part that caught my attention was when the person referred to their fish saying they had been a very bright room for a month!

I thought it was a good point and it made me think of this thread. Fish need some dark time too! I don't think they sleep, but they definitely need a little time to relax.