Another question for the brain trust.

[masraum]

You say the tank is 21.5" tall, but it seems to me most tanks don't get filled to the brim with water. And how much of the bottom is covered with gravel? I would assume that you might have 1" of free space at the top? Do you have 1" of gravel at the bottom? You'd need to subtract both of those from the 21.5". Technically, the gravel has water in and around it, but since we aren't going to compensate for the rocks/plants, lets just assume the gravel is essentially solid and the rocks plants displace the real life amount of water that's down in the gravel. So, if her tank is 21.5" tall, and we subtract 1" because it's not quite completely full, and then we subtract another 1" because the bottom is full of gravel, that would make a tank 19.5" tall. So, as stated previously 75 gallons per 19.5 inches (per means "divided by") so 3.84 gallons per inch. 3.84 goes into 15 about 4 times, so take 4" of water out and that should be about 15 gallons or 1/5 of the volume of water.

[masraum]

Originally Posted by tevake

Good idea Baz, I was helping a friend refresh the water in his tank, a large one that I had helped sort the plumbing for. And he decided to go for a bigger water change than recommended, Changed almost half the water at one time.
Next morning there were a lot of belly up fish.

Not sure what did them in, too much temp change, too much chlorine added at one time. It's a delicate ballance to maintain in a water change.
I think getting the new water close to the temp in the tank at least is a step to take.
Also some of the chlorine will off gas if left sitting out in an open bucket for a while.

Cheers Richard.

My mother used to change most of the water in the tanks that we had. She had gotten very good at it. She also eventually got up to three 20 gallon tanks. Her method was to take the fish out and put them in a bag, and float them in one of the other tanks. Then empty (mostly) that tank, clean, refill, do the chemical thing, then let the tank get to the right temp. Then she'd transfer the bag from one tank, to the other and let the bag chill in that tank for a bit. That allowed the water temp in the bag to change slowly to the overall temp and not shock the fish. Then she'd release the fish back into the newly cleaned tank. When changing water, you need to deal with the chemicals and the temp so as to not shock the fish. I'm assuming that one or both of those things got your friend's fish.

[wdfifteen]

It is amazing the roundabout way some people have tried and still managed to come up with the approximately correct solution. Steve's was the most creative, and took the longest trip into the weeds before he came back to reality.
So Glen, bottom line you're looking at about 3.75 - 4" of water depth to equal about 15 gallons.

[JackDidley]

Originally Posted by URY914

If a gold fish left from the right side of the tank at 4:15 pm and a clown fish left from the left side at 6:45 am, when would they meet?

Lunchtime, at Starbucks ??