Ph is skyrocketing. What should I do with my corydoras?

[Leopardfire]

I am starting a 20 gallon aquarium with 4 cory catfish and a betta. The tank is planted and has petco aquarium sand as the substrate. I put in the 4 cories and have just gotten the ammonia under control. When I tested the water though, it said my ph is at 9 which is WAY too high. In my other tanks, the ph stays at 7.5 so I have no idea what is wrong with my 20 gallon. Two of my cories already died and the 2 that are left are about to. They barely move and they haven't eaten in days. They're bellies look shrunken and though there's food right next to them, they won't touch it.
I'm thinking that I have to remove everything from the 20 gallon and start over. I will rinse the sand extra well in case it's leaking calcium or something. In the meantime, I'm thinking about moving my cories into a large plastic bucket. I will put the filter from the 20 gallon into the bucket to keep the ammonia under control. I am worried that the shock of going from a ph of 9 to one of 7.5 will kill the cories. They are about to die in the 20 gallon so I don't have a choice but to move them. Is there anything I can do to make the transition easier and possibly save my cories? Do you think it is already too late?

[thekoimaiden]

It could very well be the sand. I actually have special sand in one of my tanks to raise the hardness. Does the bag say it's inert? Rinsing the sand won't stop the leaking of calcium. It's the nature of the mineral makeup; you'll just have to get another bag of sand or gravel.

Do you have any other things like shells in the tank? These can also raise pH.

[Hallyx]

Keep a large bucket of that 9.0pH water. Use it to mix with your 7.5pH tapwater to slowly bring the pH down in your Cory bucket. A couple of tenths a day, if I remember correctly.

Izzy knows.

[sarahspins]

This is a known issue with the petco sand.. I found out AFTER putting it in one of my tanks, and I haven't removed it yet, but it's on my agenda. My ph has never gotten as high as yours, but it does creep up above 8 from the 7.5-7.6 of my tap water within a week.

I'd replace the substrate.. yes it's a lot of work but it's less trouble than continually having to adjust your tank's pH to compensate.

[Leopardfire]

Do you think I have to change my sand? I spent $40 on it, so I really wouldn't want to waste all that money. If it's necessary, I will remove it though. What sand could I get that wouldn't affect the ph? The petco sand was for normal aquariums, so I shouldn't have done anything. Is there any sand that is for sure safe to use as well as cheap? I don't really have a lot of money, so I can't afford anything too fancy. I need sand for my cories so I can't get gravel either. What should I do?

[thekoimaiden]

You need to make sure the sand bag specifically says INERT. Anything with oolite or aragonite will alter the water chemistry. The Tahitian moon sand should work, and I think it's found at Petsmart. It won't alter water chemistry.

[Leopardfire]

Well the bag doesn't say inert so I guess that's what caused it. Do you think play sand would be okay? I don't really want to spend another $50 on sand just yet.

[thekoimaiden]

Play sand is fine. It's what a lot of people use in their tanks. Just make sure you wash it well.

[Hallyx]

Play sand is available at Home Depot type stores. Pool filter sand is also cheap.

I'd take the sand back to Petco and raise a fuss. But that's just the kind of person I am.

[Leopardfire]

I would like to try play sand, but I'm worried that it might also leak calcium and minerals because it's cheap. Have you ever heard of this happening? I want to make sure get the right sand this time.