Sediment may have been stirred up.
That would be a standard 29 gallon aquarium
You can put one maybe 2 one-inch fishes in your one gallon aquarium
Spare parts can be bought for most of the better brands of filter. Check with a few pet shops.
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A one gallon aquarium is very difficult to maintain, however it can be done with proper filtration. An under gravel filter however does not work for saltwater very well at all. If you only use large substrate then it can work with constant water changes. I have a one gallon aquarium for a bright green mantis shrimp that I run with a small internal filter. I take a small cup of water out of it and replace it with my hundred gallon every once in a while. Tank has been up and running for almost a year now with no problem.
Its all your choice, my friend. However, the bigger the aquarium, the better the ecosystem- so I'd go with the 40 gallon. I have a 40 gallon fishtank myself.
The rule of thumb for stocking levels in a freshwater aquarium is 1 inch of fish per gallon of aquarium. For instance, five 1" guppies in a 5 gallon tank, or ten 3 inch cichlids in a 30 gallon aquarium.
Roughly 8.5 lbs per gallon. You do the Math.
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Easy. Fill the 7gal pail to the full mark (7 Gallons) with water. Then pour, from the 7 gallon pail, water into each of the 3 gallon pail up to the full mark. The remaining water left in the 7 gallon is 1 gallon. Pour this gallon into the aquarium. Fill the 7 gallon pail with water, again to the full mark, and then add to the aquarium. 1 Gallon + 7 Gallons = 8 Gallons.
You should be able to find them at the store you bought the tank from. Also most any fish supply retailer sells them. Hoods are useful to prevent water from evaporating out of your tank and to provide good lighting.
right around 400#.... water is about 8# per gallon.