If area is 18meters how much gravel I'm going to need?

You've posted this question four times without giving either the area of the hole (18 meters is a length, not an area) nor the depth of the hole. How do you expect an answer when you don't give these details?

Forget the bags-too expensive

Have a yard or two delivered from a
local building supply or borrow a pick up
& go get it

gut somethin stuck in the linkage-its under the car at the trans--if u chec it make sure u use jackstands cause a jack wil move and fall----a ride over a bummpy rode may shake it loose

There are several brand and varieties of gravel to choose from. I would be more than happy to post some of the more preferred brands here for you; however the choice is not so simple. Make sure you know what kind of gravel you need for the type of tank you have.

http://www.petsmart.com/product/index.jsp?productId=3577442

http://www.petco.com/product/112362/CaribSea-Instant-Aquarium-Crystal-River-Gravel.aspx

http://www.aquariumguys.com/gravel.html

When filling your aquarium, you will be doing so according to depth. Most people prefer a 2" depth of gravel in their tanks. Bags of gravel/sand are sold by weight however so you will need to calculate the volume you need and multiply it by the weight of a liter of the gravel you choose.

Yes, if there is no gravel in your aquarium, there are not bacteria colonies because they can only thrive in gravel environment, therefor you need to replace the water more often.

First it is important that you run your new filtration system for about one month, keeping the under gravel system in place. After a months' time, you should start by siphoning all of the water out of your tank into buckets and place fish inside buckets too during this process. Next you will need to scoop out the gravel to allow you to remove the filter. Rinse the gravel before putting it back to remove all waste.

You have a few different options for cleaning the gravel inyour aquarium:1. 1. Remove the gravel from the aquarium and washit thoroughly in a strainer, under warm tap water. Depending on the number of fish you have,this should generally be done once every other week. Do not wash the gravel with any chemical orsubstance as this could be damaging to the fish!2. 2. Use a store bought orhomemade gravel/substrate vacuum. Thisallows you to clean the gravel without having to remove it from the tank.3. 3. Use only a thin layer of gravel on the bottomof your tank and exchange with new gravel each time it needs to be replaced.

1. Remove the grass in the area

2. Place a border around the edge if desired. You could use wood, but there are several attactive edging materials available.

3. Place black plastic or a weed barrier fabric down on the dirt. the fabric would be best.

4. Place the gravel on top of the barrier to the depth you desire.

5. You will need approx. 4 cubic feet of gravel for 1" or one latrge wheelbarrow load. I suggest you think about 1.5 to 2 inches in depth tho. That will work better in th loing run

Transducers can read to an approximate depth of 18meters per watt. Hope this helps you.