PAR Inconsistency Question

[mswanson515]

Hey everyone! I checked some PAR levels in my tank and got some really weird results. Was hoping others here might be able to help with some sort of explanation.

The tank is a standard 55 gallon aquarium with 3 Hydra 26HD hanging over it evenly spaced across the top as shown in the picture. They are hanging about 13" above the water within a canopy.

I'm less concerned about the relative values as I know I can get higher numbers by lowering hte lights and such. I am, however, perpexed as to why the PAR is about 50 units higher on the sand as opposed to ont he rock adjacent to it. I would expect the values to be either the same or a little stronger on the rock since it's technically higher up in the water column than the sand level. I've marked the PAR readings on the attached picture as well.

The only thing I can figure is reflection from the glass and the sand account for the higher value since the measurements on the sand were taken closer to the glass and hte rock was taken dead center of hte aquarium. Would this be accurate or is something else going on that I'm missing?

 

[Waters]

You are exactly right.....the light reflects off of the glass and light colored substrate. Water movement at the top will also mess with the readings. Could also be the angle of the lenses pushing out rather than directly down.

 

[mswanson515]

You are exactly right.....the light reflects off of the glass and light colored substrate. Water movement at the top will also mess with the readings. Could also be the angle of the lenses pushing out rather than directly down.

Yeah, I turned off my pumps and all so there was no water movement to try to keep as many variables consistent. I just wasn't expecting such a large difference. The PAR on the sand is almost as high as only a few inches below the surface.

 

[BeanAnimal]

Yeah, I turned off my pumps and all so there was no water movement to try to keep as many variables consistent. I just wasn't expecting such a large difference. The PAR on the sand is almost as high as only a few inches below the surface.

The numbers don't mean anything.... really at all. Yes, there are reflections off of the sand, glass and rocks. That will change over time. Likewise do you (or anybody else) grow coral with the pumps off? No... so why measure light with the pumps off?

PAR meters are useless for what most of you folks think you are using them for.... all because the trend is in this hobby is to tell people they need a PAR meter to be successful. It is ridiculous.

 

[mswanson515]

The numbers don't mean anything.... really at all. Yes, there are reflections off of the sand, glass and rocks. That will change over time. Likewise do you (or anybody else) grow coral with the pumps off? No... so why measure light with the pumps off?

PAR meters are useless for what most of you folks think you are using them for.... all because the trend is in this hobby is to tell people they need a PAR meter to be successful. It is ridiculous.

I'm not using it as a tell-all metric to tell me exactly where to place stuff and can it support this or that but rather a tool to gather data to better inform me of my overall system function and metrics. That's why I'm not particulary concerned about each individual number as much as I am the relationship between the various readings in the overall system. It also doesn't mean I'm going to go out and completely rearrange my rockwork to fit some magic formula because the meter says so.

It does, however, tell me that the sand is reflecting WAY more than I originally thought it would. It also gives me additional information to consider if/when I need to troubleshoot issues that may be related to lighting.

It's not ridiculous when you use it for what it is...one tool in a larger bag of tools at your disposal to ensure the overall health of your livestock. I've been successfully reefkeeping for 20 years and never used a par meter but appreciate as much data as I can get to make informed decisions on the overall health of my reef.

 

[BeanAnimal]

It does, however, tell me that the sand is reflecting WAY more than I originally thought it would. It also gives me additional information to consider if/when I need to troubleshoot issues that may be related to lighting.

To what use? As your tank ages the rock will darken. The sand will to to an extend. Areas of the sand will have coral and the rock will have coral shadowing the sand. The flow will be on... the water will likely have tannins in it

It's not ridiculous when you use it for what it is...one tool in a larger bag of tools at your disposal to ensure the overall health of your livestock. I've been successfully reefkeeping for 20 years and never used a par meter but appreciate as much data as I can get to make informed decisions on the overall health of my reef.

I feel that it being a "useful tool" in the tool box is fallacy. PAR meters are grossly misunderstood and misused in context to coral placement, overall suitability or intensity as it relates to coral and/or to compare different setups.

"Heat mapping" your tank? Sure... but a $10 lux meter could do the same thing.

There is no such thing as a coral PUR meter... but such a tool could be very useful.

 

[mswanson515]

To what use? As your tank ages the rock will darken. The sand will to to an extend. Areas of the sand will have coral and the rock will have coral shadowing the sand. The flow will be on... the water will likely have tannins in it


I feel that it being a "useful tool" in the tool box is fallacy. PAR meters are grossly misunderstood and misused in context to coral placement, overall suitability or intensity as it relates to coral and/or to compare different setups.

"Heat mapping" your tank? Sure... but a $10 lux meter could do the same thing.

There is no such thing as a coral PUR meter... but such a tool could be very useful.

Again, it's a tool in your bag to troubleshoot overall health. Of course conditions change and of course you retest to measure trends over time. I find very little difference in this as compared to testing any other metric in your tank. You don't test your nitrates after a compelte cycle and then use that data to troubleshoot your algae issues months later. You retest to get updated readings as conditions have changed. After your water change you test the level are low but then after a few days they creep up again. You don't just do another water changes to remove the nutrients because the readings are high in your tank and low in your new salt water. You do an investigation into what's feeding the nitrates in the first place. Again, a tool in the bag of overall system health. It's all in how you use the data along with well know research by other successful hobbyist and biologists.

 

[BeanAnimal]

Again, it's a tool in your bag to troubleshoot overall health.

Again - overall health of what in what context?

Of course conditions change and of course you retest to measure trends over time. I find very little difference in this as compared to testing any other metric in your tank.

But they are different. You measure Ca to directly adjust Ca, You measure Ammonia directly to compare to known values... even if you disagree regarding the acceptable level of those values for various organisms, etc.

What useful metric are you measuring with PAR (PPFD) that lumens would not also indicate... think about that before answering.

You don't test your nitrates after a compelte cycle and then use that data to troubleshoot your algae issues months later.

You are conflating the types of data being discussed. You measure nitrate as a direct indicator that provides actual actionable data.

Again, a tool in the bag of overall system health.

Please explain what exactly the tool is useful for on context to you or the average reef aquarist. I would be more apt to label it an expensive and mostly useless toy.


Let me make two quick analogies (not perfect, but illustrative).

****************************
All Skittles
Blue
Red
Orange
Green
Yellow
Purple
Pink
Voilet

Blue, Pink and Violet are not relevant, (they have no nutritional value at all) but Red, Orange, Green, Yellow and Purple do have nutritional value for some creatures.

However - Humans can only digest Red Green and Purple. The others (Orange and Yellow) are not useable but because they have nutritional value for some creatures that digest and use them, our "skittle meter" counts them.

Jar 1 contains:
Red 150, Orange 150, Green 50, Yellow 100, Purple 50 - the skittle meter reads 500. You only can use 250.

Jar 2 contains:
Red 175, Orange 50, Green 100, Yellow 50, Purple 125 - the skittle meter reads 500. You can use 400.

So the skittle meter reads the same for both, but there is a tremendous difference in what is actually usable because the skittle meter lacks important information about WHAT skittles.
*******************************

Or another simplified way to think of "PAR" would be like "Calories". A "calorie meter" does not tell you how healthy a diet is because a diet is comprised of Fat, Carbohydrates and Proteins and to that end even subsets of those in different complexities.

So If I am on a 2,000 calorie diet that is split evenly between Carbs, Protein and Fat and you are on a diet that is 2000 calories of just Portein, our health outcomes will be drastically different and the "calorie meter" is mostly useless, as it lacks critical information about WHAT calories.

It is my opinion, based on what is being measured, that PAR meters are mostly misused and misunderstood toys. Sure, they provide a bit more meaningful number than lumens, but not really by much.

Please take a look at the chart below for a real world illustration

You have two EXTREMELY different lamps graphed above. Both put put ~125 PAR. Rest assured, given two identical tanks, one with each lamp growth and pigmentation will be vastly different and on the "edge" one lamp may support health coral and the other will not.

More to digest. That was the SAME rig and SAME meter with as many variables removed as possible. If two random reefers had one of those bulbs each and measured them in situ, with the SAME exact model of meter (sensor and software) the results would certainly differ by 25% (or far more). So one reads ~95 and the other ~123. Add in the fact that two different generations or brands of meters are likely used and the numbers can easily be 50% different... maybe 90 and 180...

I hope that makes some sense. I am not sure what 99.9999% of the people in this hobby gain be taking or comparing "PAR" numbers. They don't really correlate to useable data in most instances.

 

[mswanson515]

I don't disagree with you on many of those points. You are absolutley right and I can run my ammonia tests and compare them to yours and use that to strive to have 0ppm of ammonia. But as you pretty much pointed out, it would be misuse if I were to take my PAR readings and compare the numbers to those put out by BRS or any other hobbyist out there. As I stated earlier, it's HOW you use the data. If you simply see someone else say "Acros need 350 PAR to survive" and you strive to hit 350 PAR and ignore calcium, Nitrates, Magnesium, etc then you're not using the tool properly. Use an anemone as an example, you might get away with a lower than "average" PAR to keep yours healthy. I see it and put the same 'nem in my tank it might die at the same PAR because I'm not feeding it meat on a regular basis to compensate for lower light like you are. So only using the numbers as a direct comparison would be improper use of the data. It's much like Calcium. Your tank might need far more calcium than mine does right now because you have wall to wall Acros and huge LSP corals on the sandbed. Should I strive to hit the same number on my calcium tests as you? Not necessarily, that would be ridiculous. But should I measure the calcium and try to hit a know range in conjunction with a well established range of ALK levels to support it based on my specific coral load? Absolutely.

In my specific example, I assumed (incorrectly) that the PAR levels on my sandbed were lower than on the rock right above it since it was further away from my lights. Does that mean I'm going to move all of my Acros down there and off of the rock now that I have some numbers? No, but it does give me some data to make some potential educated adjustments to my lighting arangement to see if I can potentially even out the values from one point to another to better blend hot spots. Maybe paint the back glass to lower the reflective qualities, maybe paint the inside of my canopy to reflect light in a different way? When I make those changes I can then remeasure and see what it did to the overal PAR in the tank and use that data to know how my tank responds to such changes. I knew glass reflected light in my tank as it does in all tanks but I was unaware as to how much it reflects. I didn't think it would have the difference in values that it does. That also gives me data that I can possible "cheat" some corals and such closer to the glass to possibly grab more light when I add some more down the road.

PAR is not necessarily an absolute value that anyone should put the same weight into as something such as Calcium, Ammonia, or other metrics but it's still metrics that have some value especially when you compared it to not having the data at all. Measuring and using PAR values in and of itself is not ridiculous, it's all about how you read and use the data.

 

[BeanAnimal]

I don't disagree with you on many of those points. You are absolutley right and I can run my ammonia tests and compare them to yours and use that to strive to have 0ppm of ammonia. But as you pretty much pointed out, it would be misuse if I were to take my PAR readings and compare the numbers to those put out by BRS or any other hobbyist out there.

Thank you - and this basic scenario is what 99.99% of the folks use them for — and think they are.

As I stated earlier, it's HOW you use the data. If you simply see someone else say "Acros need 350 PAR to survive" and you strive to hit 350 PAR and ignore calcium, Nitrates, Magnesium, etc then you're not using the tool properly.

There is need to bring anything else into the conversation. 350 “PAR” which is actually 350 PPFD is a rather meaningless number given that it can’t tell is PUR, or even be used to approximate it very well.

In my specific example, I assumed (incorrectly) that the PAR levels on my sandbed were lower than on the rock right above it since it was further away from my lights.

But why use an expensive PAR meter for this outside case when a far less expensive lux meter would suffice for relative light levels? No need to answer, it is a rhetorical question.

it's still metrics that have some value especially when you compared it to not having the data at all.

Again, I simply don’t agree in context to what people use them for or understand them to measure.

Measuring and using PAR values in and of itself is not ridiculous, it's all about how you read and use the data.

I think I made my point in that it is ridiculous given what the overwhelming majority of folks use them for, and recommend them for. Yes there are narrow use case, but even those are dubious in reefing. It is simply the wrong tool.

Not trying to troll you, but rather simply trying to spread some common sense and dispel the misconceptions about “PAR”… as the majority of reef keepers conflate if with PUR (even if they don’t know the term).

Have a nice evening and good luck with the tank.