Affect of Water Changes on Nitrate and Phosphate Levels

[neoGeorge]

In a MACNA presentation by Triton's founder (excellent presentation), Ehsan mentions that a 10% water change would remove nitrate and phosphate levels by a corresponding amount, 10%.

But I wonder if, in fact, the reduction might be significantly larger if you're vacuuming the sand during the water change. Given all the cloudy stuff that gets vacuumed up, seems that getting rid of the murk would really help to lower nitrate and phosphate levels.

Thoughts?

 

[B-ridge]

Following

 

[Daniel91]

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[hart24601]

That is a good thought. It might not lower nutrients at the time of the w/c past that 10%, but will keep those nutirents lower in the immediate future before the detritus breaks down.

 

[chipmunkofdoom2]

What Hart said. Vacuuming the sand bed will not reduce nitrates directly. Sand beds cannot trap and hold nitrates in a significant way. Sand beds do, on the other hand, trap food and fish waste. If you don't remove the food and fish waste, it will eventually become nitrates. So, if you vacuum your sand bed today, you'll keep your nitrates from going up in the future. If you have a lot of food and waste built up in your sand bed, vacuuming it really well might cause your nitrates to trend down in the days following the change. But vacuuming in the sand bed today won't reduce your nitrates or phosphates today. Not any more than the percentage of the water change.

 

[neoGeorge]

OK, some anecdotal evidence that *may* illustrate a significant nitrate reduction with a 20% water change.

I haven't seen my lettuce nudibranch for a few days, so I'm left to assume it died or was eaten, and I tested the water yesterday afternoon and measured 40 ppm (tank is normally 10-20 ppm) using an API test. This morning I did a 20% water change with a rather thorough vacuuming of the sand and the nitrate measures about 20 ppm this afternoon. We all know how course the API nitrate test is, so this result is a bit loose, but it appears to me that the nitrate reduction was much greater than 20%.

Would be interested in seeing other's before/after results...

 

[BigJohnny]

In a MACNA presentation by Triton's founder (excellent presentation), Ehsan mentions that a 10% water change would remove nitrate and phosphate levels by a corresponding amount, 10%.

But I wonder if, in fact, the reduction might be significantly larger if you're vacuuming the sand during the water change. Given all the cloudy stuff that gets vacuumed up, seems that getting rid of the murk would really help to lower nitrate and phosphate levels.

Thoughts?

Testable nitrate and phosphate is already dissolved in the water column, so if you remove 10% of the water you are removing 10% of that. If you vacuum the sand simultaneously you can potentially remove waste that would break down into nitrate and phosphate, so there can be added benefit after that, but there is not an immediate reduction to existing testable nitrate and phosphate by vacuuming the sand. Make sense?

 

[Kscope]

OK, I tested the water yesterday afternoon and measured 40 ppm (tank is normally 10-20 ppm) using an API test. This morning I did a 20% water change with a rather thorough vacuuming of the sand and the nitrate measures about 20 ppm this afternoon. We all know how course the API nitrate test is, so this result is a bit loose, but it appears to me that the nitrate reduction was much greater than 20%

A better test would have been to test your water right before your change of 20%. Biological filtration could have removed 10% or so over night. Depending of course on how long ago your nudibranch died.

 

[DesertReefT4r]

In theory yes a say 50% water change will lower no3 and po4 by 50%. Now this is only in theory, real world results can vary due other factors. Our nutrient reduction theory only works if all the no3 and po4 is in the water and not being added by an "X" factor. For example dry rock that has a lot of dead organics deep inside the rock can release no3 and po4 into the water for a long time. So that 50% water change removed 50% of the waste from the water however the source is still there and just releases more right back into the water. So you do a water test later that day or the next day and don't see a 50% drop as the theory suggests and might assume it does not work. Anything that is a scource of nutrients not just leaching rock or sand can be a cause. A dead snail or fish ect, fish foods, algae die off, dirty filter socks or sponges, build up of waste in the sand bed, no3 or po4 in your source water. If you are doing water changes to lower po4 and its does not seem to be helping GFO is your best bet. It is constantly in contact with the water so it is constantly removing po4 as its released, as long as the GFO is fresh and replaced as needed. You can keep po4 in check with the GFO and water changes until the source runs out and sometimes thats all you can do, deal with it, manage it and wait.

 

[DivingTheWorld]

I run bare bottom and have tested Nitrate before (morning of) and after (next morning) water change and seen no appreciable difference. I vacuum up any detritis during my water change and do about 11%. That said, 10% difference would be pretty hard to test for unless you're running some crazy high Nitrate.

 

[neoGeorge]

Testable nitrate and phosphate is already dissolved in the water column, so if you remove 10% of the water you are removing 10% of that. If you vacuum the sand simultaneously you can potentially remove waste that would break down into nitrate and phosphate, so there can be added benefit after that, but there is not an immediate reduction to existing testable nitrate and phosphate by vacuuming the sand. Make sense?

Yes, I'm beginning to see the light here

 

[Stigigemla]

If You have a dead animal in the tank nitrate will go up in a few days and then slowly go back to the old value.
In the sand and the rock there is nitrifying bacteria and they break down fecus and food rests all the time producing nitrate. If you vacuum up their food they will produce less nitrate.
The nitrate level will go down a few days and then stabilize again.