rock displacement.. listen up newbies and write it down.

[ddc0715]

i am now pondering the TG in my reef? how many gallons of water do i truly have.. in the begining when i did not now what NO3 meant. i did not keep track of my water volume after aqua scapeing and adding rock.. nor did i track it after adding new rock along the way.. i did not understand how important this would be later on in the hobby..cause i was a NEWBIE.

Now that I have advanced. i am involved in a very detailed dosing regement that is dependent on nowing Total Gallons(TG). i understand the importand of this, but have no way to determine exactly how much water i truly have now. i cant just pull out all the coral cover rocks at this point. Also knowing the TG is needed to get a good accurate icp result. what i do know is this--

150 TG tank (totaly empty) 31" * 24" * 4'
55 TG sump that holds 25G of water (designed that way)
50 gallons of total water above the existing rock work in the DT.
2" deep sand bed (carib sea brand)

i have always just guessed at 150TG do you think that's a close enough approach?

how would you estimate your TG?

 

[Mikedawg]

Good post. I finally realized with my last build the importance of keeping track of how much water I used to fill the tank.

 

[fishyjoes]

If you have a high precision hydrometer (or some such device) you could measure your salinity before and after adding a precise amount of RO/DI water and calculate the total gallons based on the difference between the two measurements.

 

[PotatoPig]

For the sand:

Fill a known volume container with dry sand. Weigh it. Slowly add water until no more will go in. Weigh it again. Subtract the original weight and you have the weight of water. Use water density to calculate volume of water that fits into the volume of sand. Although depending on what you’re dosing you may wish to ignore the volume of water in the sand as it probably has low circulation with the rest of the tank.

For the rock:
If you know how many pounds of rock you added (and it’s all the same type) take a rock. Weigh it. Then get a bucket of water and weigh that. Then tie the rock to a string and lower it so it’s suspended in the water, fully submerged but not touching the bottom. Note the new weight of the bucket+suspended rock. Divide difference in weights of the bucket before and after suspending the rock by the density of water. This will give you the volume of the rock. Divide the weight of the rock by the volume of it to get the density. Multiply the weight of rock in the tank by the density to get the rock volume inside the tank. Subtract this from the filled volume.

 

[hoffmeyerz]

For the sand:

Fill a known volume container with dry sand. Weigh it. Slowly add water until no more will go in. Weigh it again. Subtract the original weight and you have the weight of water. Use water density to calculate volume of water that fits into the volume of sand. Although depending on what you’re dosing you may wish to ignore the volume of water in the sand as it probably has low circulation with the rest of the tank.

For the rock:
If you know how many pounds of rock you added (and it’s all the same type) take a rock. Weigh it. Then get a bucket of water and weigh that. Then tie the rock to a string and lower it so it’s suspended in the water, fully submerged but not touching the bottom. Note the new weight of the bucket+suspended rock. Divide difference in weights of the bucket before and after suspending the rock by the density of water. This will give you the volume of the rock. Divide the weight of the rock by the volume of it to get the density. Multiply the weight of rock in the tank by the density to get the rock volume inside the tank. Subtract this from the filled volume.

Love this, what a great way to figure sand and rock displacement!

 

[Randy Holmes-Farley Verified Community Expert]

Also knowing the TG is needed to get a good accurate icp result. what i do know is this--

Do you mean corrective doses? The ICP result itself is independent of tank volume.

I usually give a range for my estimate of my tank volume (say, 250-300 gallons) since I did not have a good way to determine or estimate it.

IMO, 150 gallons is a decent rough estimate for your system.

 

[mike550]

@david campbell I dont recall needing to know my tank volume for my ICP test since it only measures water parameter. Maybe things have changed?

For total water volume I backed into it. I measured my Alk two ways (Salifert and Hanna) then added a known amount of soda ash solution that would raise the Alk by around 0.8dKH. After about 15 min of letting the solution mix into the tank I measured the Alk readings again. Then I backed into my water volume by knowing then alk change and amount of solution I added

 

[billyocean]

I weighed my rocks when I put them in my system and know how much sand I added. Used the calculator online and 125 is closer to 110 gallons of volume with sump.

 

[KStatefan]

i am now pondering the TG in my reef? how many gallons of water do i truly have.. in the begining when i did not now what NO3 meant. i did not keep track of my water volume after aqua scapeing and adding rock.. nor did i track it after adding new rock along the way.. i did not understand how important this would be later on in the hobby..cause i was a NEWBIE.

Now that I have advanced. i am involved in a very detailed dosing regement that is dependent on nowing Total Gallons(TG). i understand the importand of this, but have no way to determine exactly how much water i truly have now. i cant just pull out all the coral cover rocks at this point. Also knowing the TG is needed to get a good accurate icp result. what i do know is this--

150 TG tank (totaly empty) 31" * 24" * 4'
55 TG sump that holds 25G of water (designed that way)
50 gallons of total water above the existing rock work in the DT.
2" deep sand bed (carib sea brand)

i have always just guessed at 150TG do you think that's a close enough approach?

how would you estimate your TG?

I would think that would be a good estimate of total volume.

I have a 100 gallon tank, sump and refugium and when I originally added water it took 100 gallons.

and even if you are off 10% it is not going to make that much difference and probably inside the error range of test kits.

 

[ddc0715]

ok so 500 mls of mg raised my mg by 48 ponts. from (1216-1264) apex tested .i have a 150TG tank with EXACTLY 25gs in the sump or 175TG. i played with the calulater until i found the dose i used in the results I just mentioned.

Is it logical to say my total water volume is really 129.5 tg gallons? or 150tg minus rock work. im going to test this. im shooting for 1300. reverse engineering at its finest. HAHAHAHAHA

 

[MikeG]

I have always just used a measured changes in value based on a known dose of any product. That is my reference for next time. Tanks with a super heavy coral load will always be changing in total water volume over time based on coral growth. Can’t ignore the water volume displaced by corals when is some systems that is substantial.