John P Coates
Member
Hi Sacha,
When seneye refer to a link, is that the information you have quoted in your post or was there anything else?
It does seem odd that, two years ago, seneye were saying that a KH of 5dH might pose a problem.
JPC
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Seneye
- Thread starter tubamanandy
- Start date
When seneye refer to a link, is that the information you have quoted in your post or was there anything else?
It does seem odd that, two years ago, seneye were saying that a KH of 5dH might pose a problem.
JPC
John,
This is the link to which the email refers:
http://answers.seneye.com/en/water_chemistry/what_is_pH/effect_of_ionic_strength_on_PH_tests
This is the link to which the email refers:
http://answers.seneye.com/en/water_chemistry/what_is_pH/effect_of_ionic_strength_on_PH_tests
GlassWalker
Member
Do the lower models have the light sensor physically built in then?
On the directionality of it, I think that was a design feature. The idea being you only measure light from a particular direction so you don't get influence from elsewhere. Of course downside is the readings will generally be low in a normal mounting position.
On the directionality of it, I think that was a design feature. The idea being you only measure light from a particular direction so you don't get influence from elsewhere. Of course downside is the readings will generally be low in a normal mounting position.
John P Coates
Member
If that were the case, the substrate of my freshwater tank would be covered with algae. It isn't. You have to take my word for it - but I will add a photo, if necessary. Granted, seneye refer to my unit as a reef monitor but then say that it is ideal for planted tanks.
JPC
GlassWalker
Member
I never knew that! I never liked crippleware. I assume the firmware in the unit identifies itself differently, so that the software knows which unit it is, and what to do with it. If anyone wants to try hacking, that would seem like a good starting point.
On the light and algae thing, that previous reply also mentioned reefs so things likely work differently there. Certainly I have coralline algae everywhere on one of my tanks, except the rocks for some reason...
John P Coates
Member
Yes, the problem is that the readings are so low as to be worthless. Right now, my seneye reef monitor is showing a PAR reading of 0.2 but if I orientate it towards the light source it will be between 20 and 30. So, the sensor is seeing less than 1% of the light that is falling on that point in the tank. Consequently, it would not be possible, for example, to warn me of reducing light output from a fluorescent tube that was past its 'use by' date.
JPC
John P Coates
Member
I ought to say that, overall, I do like using the seneye monitor despite its shortcomings. If I were to score it, I would give it 6.5 out of 10 points. My frustration is that the company is too small to respond in a reasonable timescale to the current products' shortcomings. They are currently focussing a lot of effort on their latest development, the SWS. Meanwhile, there are other higher priorities, such as those we're discussing here, that are falling by the wayside. The seneye monitor has massive potential and I hope one day to score it at least 9 out of 10.
JPC
JPC
Hi all,
Not so sure about this however, seems to contain a certain amount of scare mongering and urban myth, and doesn't exactly fill me with confidence:
cheers Darrel
Fair enough, at least they are honest about why there are problems with pH measurement in water with low conductivity ("ionic strength").
Not so sure about this however, seems to contain a certain amount of scare mongering and urban myth, and doesn't exactly fill me with confidence:
<http://answers.seneye.com/en/water_chemistry/what_is_KH%2C_%C2%B0KH%2C_dKH%2C_Carbonate_Hardness%3F>
cheers Darrel
John P Coates
Member
Hi Darrel,
Something here doesn't tally.
Although the water in my tank has a KH = 5°dH, it does not have low conductivity/ionic strength. I start with RO but, after adding salts, the resultant water has a conductivity of around 400 microSiemens and GH = 8°dH. We need to explore this further.
JPC
Hi all,
There are some more bits here <what is KH.....>, which suggest adding baking soda (sodium bicarbonate (NaHCO3)) to raise your dKH, all of which suggests to be that the author comes from a Marine, or Rift Lake Cichlid, keeping background, and has extrapolated from those situations to cover the very different water chemistry in planted tanks etc.
The <Strange pH readings - Seneye> page is also quite informative,
This will work quite well in heavily buffered systems (Marine, Lake Tanganyika) where large changes in water chemistry are needed to alter an intrinsically stable alkaline pH reading, but doesn't have the scale or resolution to deal with softer water, or the rapid pH changes caused by altering the CO2 ~ HCO3 equilibrium when you add pressurised CO2.
Probably the easiest way to think of the Seneye data is as a "Universal pH paper" reading presented using computer graphics.
cheers Darrel
OK that covers the "low ionic strength" issue fairly fully, and we can discount that. I've had a look at the pages on the pH pages Seneye site <what is pH - Seneye> and it is quite good as a description (he also uses the "balance" analogy as well), but the bizarre thing is that having told you that pH is a moveable feast where you have very little buffering, he then goes onto tell you that "pH swings, pH crashes and fish death" will occur in soft water because tiny changes in water chemistry will have huge effects on pH! I'm not quite sure what to say at that stage, other than "failed to join the dots together".
There are some more bits here <what is KH.....>, which suggest adding baking soda (sodium bicarbonate (NaHCO3)) to raise your dKH, all of which suggests to be that the author comes from a Marine, or Rift Lake Cichlid, keeping background, and has extrapolated from those situations to cover the very different water chemistry in planted tanks etc.
The <Strange pH readings - Seneye> page is also quite informative,
So that accounts for the slide bit, basically we are talking about the Seneye unit using colorimetry to read the colour change of a universal pH indicator fixed to a slide.
This will work quite well in heavily buffered systems (Marine, Lake Tanganyika) where large changes in water chemistry are needed to alter an intrinsically stable alkaline pH reading, but doesn't have the scale or resolution to deal with softer water, or the rapid pH changes caused by altering the CO2 ~ HCO3 equilibrium when you add pressurised CO2.
Probably the easiest way to think of the Seneye data is as a "Universal pH paper" reading presented using computer graphics.
cheers Darrel
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Hi all,
cheers Darrel
Reviewing this thread, I see that I never answered this one. The pH readings in the very soft tap water are likely to be very variable, as any small changes in water chemistry will cause large changes in pH, but once the water is buffered to dKH5 you should get a more stable reading.
cheers Darrel
John P Coates
Member
Hi Darrel,
Thanks for the comprehensive reply.
So, ionic strength, per se, has no bearing on the accuracy of the seneye pH reading. As you point out, the device is using colorimetry to determine pH. If the seneye monitor cannot respond to rapid pH changes, it cannot be reliably used for pH profiling. And, if there is anything slightly discolouring the water, that will also contribute to inaccuracies. Fortunately, I use RO water as my starting point so bleaching with chlorine/chloramine shouldn't be a problem. Wahey!
JPC
John P Coates
Member
GlassWalker
Member
Before I moved the Seneye to my marine tank, it was in a hard water tank (mollies, britlenose). I did have lots of bogwood, and added alder cones, IAL, teak tree leaves too as the plecos seem to like them. I don't recall getting unexpected pH readings, but couldn't say they were verified as accurate either.
Hi all,
The wavelengths of light (in nm) are shown below with the spectral reflectance curves of the two blue colours shown (unsurprisingly absorbed mainly in the blue wavelengths of light around 475nm), you can also see a small red peak, meaning that the colours would look slightly purplish to a camera film, but not to the human eye which is very sensitive to blue wavelengths of light.
In the case of Seneye for the blue alkaline pH readings the tannins would have little effect, unless the light path was very long (and I'm pretty sure it isn't), or the water very heavily tannin stained.
The same is not true for the more acid pH colours (yellows, red and oranges) where there would be interference from the similarly coloured tannins, which would absorb at these same wave lengths.
cheers Darrel
It would probably depend a little bit on how tannin stained the water is, and also the colour of the slide. Without knowing how the slides in the Seneye are read, what would normally happen is that a specific wave length of light (in nanometres and corresponding to the colour you are interested in) would be shone through the slide, and the amount of absorbed light recorded. Presumably the Seneye unit scans at a number of different wave lengths from ~700 nm (red, acid) through green ~550 nm, (neutral, pH7) to ~450nm (blue, alkaline).
The wavelengths of light (in nm) are shown below with the spectral reflectance curves of the two blue colours shown (unsurprisingly absorbed mainly in the blue wavelengths of light around 475nm), you can also see a small red peak, meaning that the colours would look slightly purplish to a camera film, but not to the human eye which is very sensitive to blue wavelengths of light.
In the case of Seneye for the blue alkaline pH readings the tannins would have little effect, unless the light path was very long (and I'm pretty sure it isn't), or the water very heavily tannin stained.
The same is not true for the more acid pH colours (yellows, red and oranges) where there would be interference from the similarly coloured tannins, which would absorb at these same wave lengths.
cheers Darrel
Hi all,
cheers Darrel
I'm just going to correct the post above, mainly because I start writing it before I'd found a suitable image and I couldn't find exactly what I wanted, so I put in a reflectance curve, rather than an absorbance one without changing all the text. What it should say is
If we stick strictly to absorbance, rather than reflectance, the whole process would be inverted, so that the peaks on the graph become troughs and vice versa. This is why leaves are green, they are reflecting green light and absorbing light at the red and blue end of the spectrum.
cheers Darrel
