Advanced methods of maintaining nitrates and phosphates.

[tripdad]

The GHL Ion Director claims to be able to monitor nitrates automatically. If so, then this should be able to direct dosing pumps. May be worth investigating.

 

[Tampaman]

2nd overpowered refugium, i can easily fix a 0 reading, High PO and it means repeated water changes. I do direct feed when possible with the PH off...

 

[Randy Holmes-Farley Verified Community Expert]

The GHL Ion Director claims to be able to monitor nitrates automatically. If so, then this should be able to direct dosing pumps. May be worth investigating.

Chloride strongly interferes with the nitrate selective electrodes that I have seen data from. I'm not sure what levels or accuracy they claim (or if they claim it works in seawater since they also sell pond products), but I would be very wary of this method for nitrate in seawater.

 

[vahegan]

Chloride strongly interferes with the nitrate selective electrodes that I have seen data from.

They probably take account for salinity (maybe simply measure the conductivity of the sample) and based on that correct the nitrate measurement. Providing that normally the ratio of chloride ions is probably quite stable in seawater (although its content is quite high, being the most abundant ion at about 19.4g of chloride in each kilogram of seawater, followed by sodium at 10.7g/kg, sulphate at 2.7g/kg and magnesium at 1.2g/kg. The content of all other ions is significantly lower with calcium and potassium around 0.4g/kg, HCO3 around 0.13g/kg, and the rest about 0.1g/kg altogether). Thus, conductivity of seawater is mainly provided by sodium chloride and by measuring conductivity it is possible to compensate the ratio by which the chloride ion affects the nitrate measurement.

 

[Randy Holmes-Farley Verified Community Expert]

They probably take account for salinity (maybe simply measure the conductivity of the sample) and based on that correct the nitrate measurement. Providing that normally the ratio of chloride ions is probably quite stable in seawater (although its content is quite high, being the most abundant ion at about 19.4g of chloride in each kilogram of seawater, followed by sodium at 10.7g/kg, sulphate at 2.7g/kg and magnesium at 1.2g/kg. The content of all other ions is significantly lower with calcium and potassium around 0.4g/kg, HCO3 around 0.13g/kg, and the rest about 0.1g/kg altogether). Thus, conductivity of seawater is mainly provided by sodium chloride and by measuring conductivity it is possible to compensate the ratio by which the chloride ion affects the nitrate measurement.

In reef tanks, chloride varies outside of salinity as well. In part that is from unbalanced chloride additives such as calcium chloride without offsetting sulfate.

 

[vahegan]

In reef tanks, chloride varies outside of salinity as well. In part that is from unbalanced chloride additives such as calcium chloride without offsetting sulfate.

Yes, indeed, if Part 3 is not used, and no significant water changes are made, the ratio of chloride may change with time to some extent (BTW, do you know if maintaining the exact ratio of sulphate to chloride is that important for the reef? Why I am asking is because I was thinking that if we reduce the sulphate ratio in reef water /e.g. only use magnesium chloride for part 3/ it will be easier to maintain higher Ca levels in the tank because its precipitation in the form of calcium sulphate will be reduced). However, since sodium chloride is the main factor accounting for seawater conductivity, a slight change of its ratio to magnesium and sulphate ions should not result in a too significant error if we try to compensate for chloride baed on conductivity readings. It is probably possible to estimate this error but for this we need to know how much the change of chlorides will affect the readings of ion-selective electrode for nitrate...

 

[Randy Holmes-Farley Verified Community Expert]

Yes, indeed, if Part 3 is not used, and no significant water changes are made, the ratio of chloride may change with time to some extent (BTW, do you know if maintaining the exact ratio of sulphate to chloride is that important for the reef? Why I am asking is because I was thinking that if we reduce the sulphate ratio in reef water /e.g. only use magnesium chloride for part 3/ it will be easier to maintain higher Ca levels in the tank because its precipitation in the form of calcium sulphate will be reduced). However, since sodium chloride is the main factor accounting for seawater conductivity, a slight change of its ratio to magnesium and sulphate ions should not result in a too significant error if we try to compensate for chloride baed on conductivity readings. It is probably possible to estimate this error but for this we need to know how much the change of chlorides will affect the readings of ion-selective electrode for nitrate...

I do not think the exact ratio of sulfate to chloride is critical for reef health, and that is good because results from icp testing show some fairly substantial variability. Even some salt mixes seem to start with off ratios.