Test Kits

[Drez]

Do aquarium test kits (i.e. Aquarium Pharmaceuticals pH etc.) take into account the water meniscus when filling to the line? I would think not since the average aquarist isn’t a seasoned chemist and wouldn’t think about it so I would assume they would thus raise the line so that it’s slightly higher then 5ml (accounting for the water meniscus). However, I fill mine with a syringe for 5ml and it is actually higher then the line (5-10%). This is enough to impact measures like kH and Ca a lot since they’re based on adding drops to get the amount in your tank. What do you guys do / think? Is it too trivial to matter?

[newjerseynano]

i dont think Aqua pharm is really that accurate to matter whether it is a mm higher. Salifert might be, or some other lab grade kit, but i wouldn't worry about it. And i honestly think it might vary any of the tests maybe a half a mark, so dont worry about it. like if your ph was 8.7, its prob 8.6-8.8, but in either case, your tank is in trouble.

 

most important test imo is salinity. just do your w/c s and test salinity everyday and you should be good (salt takes care of the ph, calc, etc) for a cube. hth

[Drez]

I've heard this but I've tested my mixed water and it's still way low in Ca. I mixed IO salt to 1.024 SG for 24 hrs and read Ca in the hi 200's. Bunk salt or test kits?

 

Sigh, if I had a grand to spare I'd go and get lab grade pin point monitors for all my tests:(

[ChemMan]

Typically you fill so that the bottom of the meniscus is level with the line on the vial. I highly doubt that any test kit you can buy will be accurate enough to be affected by the meniscus level. Drez, check your Mg, it will probably be too low. I use IO salt and my Mg is 300 ppm, and it should be ~1300 ppm. Too low Mg can keep you from getting your Ca right, no matter what how much you put in.

[newjerseynano]

yea IO is def always low in calc, because of the magnesium levels chemman stated. if you corals are doing fine, i wouldnt worry about it. but if they are suffering, try checking for mg, then if its low boost it with a supp. then chek calc and if its still low check the alk level. always check these both first as they are all connected, as in a low alk or mg will yield low calc no matter how much calc u add (i think, correct me if im wrong). hth

[donnoj]

I use Tropic Marin sea-salt and test every box when I do my first mix. It tends to be low in Magnesium and Calcium. I calculate the deficiency for each box and add supplements every time I mix a batch to make up the difference.

 

I use Salifert for all my tests except PH and Salinity. For those I use an electronic PH meter and refractometer.

[ChemMan]

yea IO is def always low in calc, because of the magnesium levels chemman stated. if you corals are doing fine, i wouldnt worry about it. but if they are suffering, try checking for mg, then if its low boost it with a supp. then chek calc and if its still low check the alk level. always check these both first as they are all connected, as in a low alk or mg will yield low calc no matter how much calc u add (i think, correct me if im wrong). hth

 

Mg bounds with carbonate ions in preference to Ca. Low Mg means that the Ca in your water is mainly bonding with carbonate ions and becoming insoluble Calcium Carbonate, which then drops out of the water column. Essentially the Calcium no longer exists. With enough Mg, the carbonate ions bond instead with the Mg, and the Ca remains free for use by your corals, etc. I think that pretty much sums it up.

[Drez]

Thanks all this has been helpful.

Lets see if I have this right now then. So in summary.

 

1) Don't worry about the meniscus, fill it with a true 5ml by syringe or to the line so that the meniscus dip meets the line, any inaccuracy beyond that is irrelevant as the tests aren't that accurate anyway.

 

2) Use Salifret were possible or pinpoint when $$ allows

 

3) Test Mg levels. If they are low supplement wait and test to see if kH and Ca levels are corrected by this. If not supplement Carbonate and Ca.

 

 

One more question, if the IO salt is low in Mg from the start, then as soon as it is mixed the Ca will start binding with carbonate depleting hardness and Ca levels, so even if Mg is added afterwards both Ca and Carbonate will still need to be dosed to some degree (based on the speed of the reactions). Does this mean I will/should just be adding these to my mix or can I add the Mg to the salt right when I'm mixing to try and prevent the whole thing initially? I know as a rule salt should be mixed first to avoid unwanted chem reactions.

 

thanks

[newjerseynano]

you could mix the supplement right in to your mixed sw, thats what i do sumtimes.

[Drez]

Right as your mixing the salt or after the salt have been fully disolved?

[Reef Gator]

One more question, if the IO salt is low in Mg from the start, then as soon as it is mixed the Ca will start binding with carbonate depleting hardness and Ca levels, so even if Mg is added afterwards both Ca and Carbonate will still need to be dosed to some degree (based on the speed of the reactions).

 

Drez,

 

That's actually not quite right. Calcium carbonate is not completely insoluble (no ionic crystal is), there is an equilibrium between the solid and dissolved forms. Higher Mg will shift this equilibrium towards the dissolved form. So dosing Mg equals higher dissolved Ca and carbonate regardless of the physical form prior to dosing. You still may need to dose Ca and carbonate depending on the needs of your corals of course.

[Drez]

Drez,

 

That's actually not quite right. Calcium carbonate is not completely insoluble (no ionic crystal is), there is an equilibrium between the solid and dissolved forms. Higher Mg will shift this equilibrium towards the dissolved form. So dosing Mg equals higher dissolved Ca and carbonate regardless of the physical form prior to dosing. You still may need to dose Ca and carbonate depending on the needs of your corals of course.

 

Gotcha, thanks for the clarification. I didn't know that the precipitates formed would reverse with added Mg. So add Mg to salt water after its mixed, test Alk and Ca and add accordingly to get desired levels. For future mixes keep track of amounts needed to hit targets.

 

For those future mixes though they can't all go in at the same time though right? Salt allow to dissolve, then Mg allow to dissolve and then Ca then Carbonate (or carbonate then Ca so so long as not at the same time).