Does Flow Affect Par?

[PeterC99]

Thinking about renting a par meter but was wondering how to properly measure the par?

Does the amount of flow in an aquarium have any impact on the par? Does par change with the different flow rates from the pumps?

 

[P-Dub]

Thinking about renting a par meter but was wondering how to properly measure the par?

Does the amount of flow in an aquarium have any impact on the par? Does par change with the different flow rates from the pumps?

Yes, in so much as it will drift based on the surface agitation and refraction as a result. I measure with the flow on and keep the sensor there for a while, recording the average PAR. Par can jump around quite a bit, so pick the highest and lowest readings produced and you can surmise the average of the two for the most accurate assessment of what your corals are actually receiving. IMHO.

To satisfy your curiosity, test also with no surface agitation. Keep your sensor verticle.

 

[PeterC99]

Yes, in so much as it will drift based on the surface agitation and refraction as a result. I measure with the flow on and keep the sensor there for a while, recording the average PAR. Par can jump around quite a bit, so pick the highest and lowest readings produced and you can surmise the average of the two for the most accurate assessment of what your corals are actually receiving. IMHO.

To satisfy your curiosity, test also with no surface agitation. Keep your sensor verticle.

That makes so much sense! Thank you!

 

[Pistondog]

I would measure with the flow off to make it easier. I think the par meter will be more accurate with a steady light, vs reading the shimmer caused by surface agitation.

 

[CoralNerd]

I've been told leave the flow on. It is a pain in the but taking readings however.

 

[LDog74]

I just rented a par meter from BRS. The flow absolutely effects the par readings. I am seeing anywhere from a 20-75 difference. I have 2 MP40’s & 3 RS 45 Reefwaves on my 225 gallon for movement.
I would leave your pumps on for taking readings.

 

[PeterC99]

I just rented a par meter from BRS. The flow absolutely effects the par readings. I am seeing anywhere from a 20-75 difference. I have 2 MP40’s & 3 RS 45 Reefwaves on my 225 gallon for movement.
I would leave your pumps on for taking readings.

Thank you! That’s a significant difference!

 

[spd3001]

I've done studies of optical transmission through turbulence. Whether the medium is air, water or hot gasses it's affected by the turbulence. The medium can be modeled as a collection of many different sized lenses that appear and disappear in the line of sight. So any instantaneous measurement can be higher or lower than what would be measured in the absence of turbulence. In an aquarium, the intensity is probably varying quite rapidly depending on the strength of the flow and the nature of the boundary between the air and seawater. However, if you're taking your measurements with a handheld sensor, that probably introduces as much uncertainty in the measurement as the turbulence as it's difficult to hold the sensor stationary and parallel to the surface of the water.

 

[Aardvark1134]

Since par meters vary up to about 20% from brand to brand and model to model ...they are just giving you a rough guess anyway. It's more important to make sure you have the same brand/model/firmware version as the person you are trying to compare to.

 

[drblank1]

Thinking about renting a par meter but was wondering how to properly measure the par?

Does the amount of flow in an aquarium have any impact on the par? Does par change with the different flow rates from the pumps?

I first took measurements with the flow off and this was my baseline. Then repeated the same measurements points with flow on. With both sets of data, I was able to determine what type of coral is placed where. Maybe not the best approach but I'm a data guy so this made sense to me.

 

[davilahope]

It definitely affects par!! I've actually had an acro that got burnt from me leaving the flow off for too long because it was receiving more light than usual for that unknown amount of time

 

[Laith]

I measure with normal flow on. Measuring with flow off is not going to show you the PAR levels when the tank is running normally...

 

[Maximitsurugi]

I spoke to a YouTuber about testing par with flow on and off. His experiment showed a negligable difference while my tank tests about 50 to 70 par lower on average. The variable in my mind is intensity of flow. My surface literally boils and I generally have no flat breaks on my water surface. So what do I do? Whatever my par says with flow off, i set my light 5 or so percent above my target par.