240G with 75 sump, WHY do I still have high nitrates?

[dogofwar]

Filtration creates nitrAtes. The primary way to dilute nitrates is water changes.

I'd do a series of 75-80% water changes every other day or so for a couple of weeks to get things down to near nothing...

50% weekly water changes just won't get you there.

 

[dogofwar]

Filtration creates nitrAtes. The primary way to dilute nitrates is water changes.

I'd do a series of 75-80% water changes every other day or so for a couple of weeks to get things down to near nothing...

50% weekly water changes just won't get you there.

 

[skjl47]

Filtration creates nitrAtes.

Hello; may I ask what you mean by this. More specifically, what is the mechanism by which filtration creates nitrates?

Do you mean that if I set up a tank with a running filtration system and no fish or other living things there will be nitrates created? I predict this is not what you mean.

 

[imabot]

I think you would need a very heavily planted sump and frequent water changes for nitrates to go down. Maybe a algae scrubber?

 

[twentyleagues]

There are other ways of Nitrate removal. The best most effective way is to of coarse do water changes. The problem with water changes is its possible to add nitrates as stated above. I think the max acceptable nitrate lvl for tap water is 20ppm. I don't think Ive ever seen it that high though anywhere I know of. So you can get creep as explained by Drstrangelove and justarn good info! Running it through a ro system will fix that problem though.
Terrestrial plants/ plant filtration. Terrestrial plants remove nitrates much faster then submersed plants something to do with available c02 and the way its processed in plants not under water. Something fast growing I use Pothos, looks nice, doesn't need bright light can use ambient lighting. I do light my Pothos now and it grows very fast. I do a little larger then 50% weekly water change and with my lighted pothos I now get no more then 40ppm before water change on wc day. I am heavily stocked, and I feed heavy too.
There are bacteria that remove Nitrates, anaerobic bacteria. Lots of ways to cultivate them they are in your tank now just not in large numbers. Carbon dosing is the fastest way to do it. You need to offer bacteria a "special" place to live, a reactor, low flow low oxygen or in larger systems higher flow but still must be oxygen depleted water and an appropriate substrate. That will get a good colony on its own, but you wont see any huge drops in nitrate right away or maybe even at all based on what else is happening. That's where carbon dosing comes in, it supercharges your anaerobic bacteria! Live fast Die young! that's the problem. You need a way to rid yourself of all the anaerobic "corpses", in saltwater you use a protein skimmer. Fresh water its a little more difficult but Ive heard you can route the output of your reactor to the mechanical stage of your filtration.......
Just some other options and some that have been discussed already.

 

[dogofwar]

The nitrogen cycle... Of course a tank with no fish wouldn't have nitrates (or ammonia).

Hello; may I ask what you mean by this. More specifically, what is the mechanism by which filtration creates nitrates?

Do you mean that if I set up a tank with a running filtration system and no fish or other living things there will be nitrates created? I predict this is not what you mean.

 

[justarn]

I've seen 45ppm out the tap here in kent UK. Our legal limit is much higher than the USA at 50ppm!

 

[twentyleagues]

I've seen 45ppm out the tap here in kent UK. Our legal limit is much higher than the USA at 50ppm!

Holy moly! Levels that high have been linked to infant deaths. Wow that'd completely negate my water changes.

 

[Drstrangelove]

Drstrangelove where can i see how you get your results......as in i want to try and do my own math on my system.

It's actually this:

1) Determine the amount of protein you put in the tank in grams. You can measure this. Weigh the food, apply the dry weight %, multiply the % of protein to get grams of protein.

The dry weight % varies by food and has to be determined for each food. Basically, remove the water content since water doesn't provide nutrients. That leaves dry weight.

Since I don't have access to this (and most people don't actually track it) I use a proxy:

a) fish length (by species) = fish weight in grams. The proper method is a large sample with a likely log scale calculation, but a girth to length to weight linear method is an approximation.

b) fish weight times typical feed to weight rate (this varies by fish age) = volume of food in grams. Fry and young fish will consume more (5+% per day) than mature adult fish (1.5% per day.)

c) volume of food in grams times dry weight % times protein % = grams of protein

2) Convert (in milligrams) the protein to nitrogen to ammonia to nitrites to nitrates.

a) Protein is 82% nitrogen by weight
b) Nitrogen is 16% ammonia (this varies) by weight
c) Convert ammonia to nitrates. Ammonium x 2.7015 = nitrite; nitrite x 1.3475 = nitrate; Ammonia x 3.64 = nitrates.

This comes from the molecular mass (nitrogen is 14.00643, hydrogen is 1.00784, oxygen is 15.999)

Ammonium is NH4
Nitrite is NO2
Nitrate is NO3

Thus total weight is ~18.03779. 46.00443, 62.00343 respectively. And 1 ppm of ammonium in grams converts to 3.473 grams of nitrate.

This is because NH4 is 14.00643+4*1.00784 = 18.03779 and is converted to NO3 which is 14.00643+3*15.999 = 62.00343.


3) Determine the actual volume of water in the system in liters. 1 gallon x 3.78544 = liters of water.


4) Divide (milligrams) #2 by (liters) #3. That's the ppm of nitrate. (This is because mg/liter is the same as ppm in liquid measures.)

Calculating the peak and average ppm of nitrate over time is really just a spreadsheet, but I use this online calculator. http://www.theaquatools.com/water-changes-calculator

 

[Drstrangelove]

Just a note on the above. Step 2C says 2.7015, but should be 2.550756, while the total of 3.64 should instead be 3.4753.

That's because I used ammonia (NH3, weight 17.031, not ammonium weight 18.03779) in the formula.

If you change those 2 numbers, the math should work.