Test tube 5mL line markings

[Peter T]

Hi guys, I just ran into an issue that I should of caught quite a long time ago.

I have been using two different brand test kits for a bit now; a Salifert for Mg, Ca, and KH. They come with a 5mL baster. Then I use an API test set which comes with 4 tubes of 5 mL and tests for pH, nitrate, nitrite, and ammonia.

On a whim just now I decided to see how accurate the 5mL markings on the API test tubes are and used the 5mL baster to fill up the tubes. To my surprise, the water level was about 1 cm above the API tube's 5mL line.

Now my question is, should I use the lines provided on the test tube even though it isn't actually 5mL? Any input would be greatly appreciated, thanks!

[vivioo7]

how do u know which one is inaccurate?

[Peter T]

I would assume that the test tube is inaccurate. The basters look exactly like medical hypodermic syringes and it can fit a needle at the end if you attach it. They have clear distinct markings on them for each mL marking. The test tubes only have one line that mark the 5mL mark. I think I will pick up some medical syringes tomorrow and determine actually which one is accurate; my money is going with the baster.

Still, if the test tube markings are inaccurate, should I still use that marking when testing? Hmm... I feel like an idiot. Should of noticed this a LONG time ago!

[sslak]

It's an easy thing to test if you have a digital scale available.

1ml of pure water = 1g

So the tube should be 5g heavier when full compared to empty.

Either way, the API test kits were designed to work with the tube provided, so you should be able to use them with accurate results.

[Fishfish0001]

Yeah, I found that too, but I just use the API line, as thats what it is designed to work with. Medical Grade syringe too.

[mcoomer]

I posed this same question some time ago and the general consensus was to use the syringe as the guide. I disregard the lines on the vials.

Mike

[SushiGirl]

We got a syringe from the drugstore, and when I fill it to the 5 mL mark, it matches the 5 mL marks exactly on my API test tubes. I like using the syringe to rinse & fill the tubes so I don't have to get my fingers in there.

[Fishfish0001]

I use one from my dads vet, and it doesn't match, at all.

[pramberg]

Interesting, I never even thought to check.

[djkms]

I find the API tubes to be highly inaccurate as well. Some lines are higher than others. I too use the salifert syringe. Keep in mind the air bubble as well and the water at the tip. If you look at the syringe the 0ml of water line starts at the base and not the tip, something to account for...

[Reeftanker]

I often thought about this as well.I have the old vials from API and the line or mark is rather thick.I never really knew where to fill it to.I started using a syringe to measure the fluid.I also have the new vials from API as well ,the mark on the new ones are much thinner.With the syringe it measures right to the line on the new style,with the old its to the bottom of the line.Does it make that much of a difference??I dont know.

[GT_Jacket]

It is right or wrong to "pump" the syringe in the liquid to be measured to get all the air out 1st?

[djkms]

I honestly don't think it really matters. Hobbyist test kits are inaccurate at best. I think they are more of a "range" test then a accuracy test. I mean lets think about it. They would have to make the holes on the tip of the liquid bottle EXACT for every kit. These are mass produced and different type users are using them. There is no way to get the exact same size drop every time. If you really look at the drops before they hit the water to be tested they are different sizes. Add the way you drop it (sideways, bottle upside down, etc) The pressure you place on the bottle, airborne or contaminants left over on the test vial, etc.

[GT_Jacket]

True... but I was inquiring for one of the Zeo additives I put in at .25ml 2xdaily :)

[Fishfish0001]

These things aren't exactly accurate anyways, I mean there is a large range, so I doubt a little extra water will have any major impact on results.

[Peter T]

It's an easy thing to test if you have a digital scale available.

1ml of pure water = 1g

So the tube should be 5g heavier when full compared to empty.

Either way, the API test kits were designed to work with the tube provided, so you should be able to use them with accurate results.

Hehe yeah, I don't keep one available, but it would be a very accurate way of determining volume.. I have faith in the medical syringes measurements though. Imaging the lawsuits if someone overdoses on medication.

I find the API tubes to be highly inaccurate as well. Some lines are higher than others. I too use the salifert syringe. Keep in mind the air bubble as well and the water at the tip. If you look at the syringe the 0ml of water line starts at the base and not the tip, something to account for...

Thanks for the heads up! I already knew that though :fun2:

It is right or wrong to "pump" the syringe in the liquid to be measured to get all the air out 1st?

Hold the syringe upside down (needle tip facing up) and tap the syringe so all the air bubbles rise to the top. Then depress the syringe so it squirts a stream of water. Their is a "buffer" space between the full syringe and the 5mL line so you can get rid of all the air.

These things aren't exactly accurate anyways, I mean there is a large range, so I doubt a little extra water will have any major impact on results.

It throws my pH reading from 8.2 to 8.0. I mean both are acceptable, but I would like a reading as close to exact as possible.

Thanks for all the responses guys, I really appreciate everyone of them. By the way, I did check the Salifert syringe and it is accurate when measured with a medical syringe. I think I will use the 5mL syringe for measurements until I finish with this API test kit and buy the newer test kits. Plus it reads my nitrates at 0 instead of 5-10 (colors are so hard to distinguish!) :lolspin:

[Amp2020]

The test tubes are just cheap productions that couldn't care less how accurate they are. I've wondering if the test tubes were just defective tubes that are sold to the aquarium industry at cheaper rates. I always use a medical syringe when measuring unless I know that the lines on the tubes are accurate.

[allsps40]

API vials are off. I use a 5ml syringe.

[Everyones Hero]

It is right or wrong to "pump" the syringe in the liquid to be measured to get all the air out 1st?

I don't. I set the syringe to 0mL, put the tip in the water & draw to the 5mL mark. There will be air between the water & plunger but the water in the tip (from the 0mL mark to the tip) will make up for that. Then I push the water into the test tube. That will be 5mL (or as close to 5mL as the syringe is marked.)

When I'm adding the chemicals while doing the tests I hold the bottle completely vertical. It's supposed to insure the drops are uniform.

Not that this is an exact science but I try to practice the techniques I learned in school.