Water Changes/PH questions - The Planted Tank Forum
Old 02-01-2004, 04:26 AM Thread Starter
Planted Member

Join Date: Dec 2003
Posts: 183
Well I gotta admit I just don't know how much water my gravel displaced, but I have about 50 lbs of pea gravel in my 29 gallon. So I have been unsure as to the actual volume of my water. Does anyone know what this might be, or a rough guess?

So I am going to be using a python like device to do my water changes now. Before I could just dump the water into a 5 gallon bucket and now approximately how much water I was taking out. With the python I cannot do this. Is there a way to do calculate how many inches from the top would get me a certain amount of gallons taken out of my tank. The other thought I had was to do a water change the old way with buckets and then at the end mark on the tank how low the water is from the amount I have taken out.

Also with the advent of pressurized for my tank, the ph is now at around 7.0, my tap is at 7.5 will a 50% water change with the tap raise the ph too high for the fish to handle?

Thanks in advance for all help!

29 Gallon Standard Moderate Light Planted tank
Lighting: 2x27 Watt 6500k P.C. Lights of America Outdoor Fixtures. 2x 20 Watt N.O. Flor. w/ Sylvania Gro Bulbs (9350k I think). Both are retrofited into a diy 12" tall canopy, with a 4" Diameter Clip on fan facing the opening in the back to circulate the excessive heat from the lighting.
Filtration: Tetra Tech 150 (modified to make very little disturbance.
Aquarium Systems Mini-jet for more circulation.
plantastic28 is offline

Old 02-01-2004, 04:39 AM
Planted Tank Guru

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Location: Portland Orygun
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Just running the math gives this result. 5 gallons of water is 1155 cubic inches of water. In a 30X12 tank that means that 3.2" of water is just about 5 gallons.
Rex Grigg is offline
Old 02-01-2004, 04:41 AM
Planted Tank Guru

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Do you know what the actual resting pH is of your tap water? If not then pour some water into a cup and test it 12 and 24 hours later. If your true pH is 7.5 and the tank is 7.0 then a 50% water change is not going to be a problem for the vast majority of fish.
Rex Grigg is offline

Old 02-01-2004, 05:25 AM Thread Starter
Planted Member

Join Date: Dec 2003
Posts: 183
Will do thanks Rex!!

29 Gallon Standard Moderate Light Planted tank
Lighting: 2x27 Watt 6500k P.C. Lights of America Outdoor Fixtures. 2x 20 Watt N.O. Flor. w/ Sylvania Gro Bulbs (9350k I think). Both are retrofited into a diy 12" tall canopy, with a 4" Diameter Clip on fan facing the opening in the back to circulate the excessive heat from the lighting.
Filtration: Tetra Tech 150 (modified to make very little disturbance.
Aquarium Systems Mini-jet for more circulation.
plantastic28 is offline
Old 02-01-2004, 01:17 PM
Algae Grower

Join Date: Dec 2003
Location: new ulm, mn
Posts: 122
you do not really need to know gallons per inch in order to measure out a certain %. for example, lets say your tank is 20" from top of gravel to top of water level. 20% of 20" is 4" so, if you take your water level down 4" you should have removed ~20% or your water.

i just put a mark on the side of my tank indicating the water level to bring it down to utilizing the methodology above.
quilaho is offline
Old 02-01-2004, 01:54 PM
Planted Tank Guru

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That would work on a empty tank but you need to take into account the water displaced by the substrate which can be quite a bit in a planted tank with a deep substrate.
Rex Grigg is offline
Old 02-01-2004, 03:55 PM Thread Starter
Planted Member

Join Date: Dec 2003
Posts: 183
Rex,

Just for my own future reference on other tanks, what formula did you use to get that information?

Thanks.

29 Gallon Standard Moderate Light Planted tank
Lighting: 2x27 Watt 6500k P.C. Lights of America Outdoor Fixtures. 2x 20 Watt N.O. Flor. w/ Sylvania Gro Bulbs (9350k I think). Both are retrofited into a diy 12" tall canopy, with a 4" Diameter Clip on fan facing the opening in the back to circulate the excessive heat from the lighting.
Filtration: Tetra Tech 150 (modified to make very little disturbance.
Aquarium Systems Mini-jet for more circulation.
plantastic28 is offline
Old 02-01-2004, 04:20 PM
Planted Tank Guru

Join Date: Dec 2002
Location: Portland Orygun
Posts: 9,600
Well I used Master Converter to change gallons into cubic inches and then took the measurements of a 29 gallon tank 30"x12" nominal. then I took the result of the gallons to cubic inches and divided it by the result of the nominal tank size. That gave me the answer.

Also one could compensate for the substrate by a simple test. Take container that holds a known amount of water. In this example let's say 3 gallons. Fill this container with water. Now put this container in a larger container. Now take a sample of the substrate in question and pour it into the first container. Then measure how much water was displaced. So a clear example, I have a 10 gallon tank. I'm going to use one bag of Flourite in it. So I take 1.5 lbs of the Flourite and add it to a filled one gallon container and then measure the displaced water. Let's say it's two cups of water. So I can then figure that the whole bag in a 10 gallon tank is going to displace around 10 cups or 1.25 gallons of water. This gives me a nominal tank volume of around 9 gallons since a standard 10 gallon tank actually does hold very close to 10 gallons of water, unlike some tank sizes.
Rex Grigg is offline

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