Hi all,

Understand that PAR is a better measure of light intensity that plants need.
Has anyone tried measuring at which PAR does any particular plant grow faster?
I have HC in a 3wpg (18inch deep) tank. I didnt see any difference in growth rates even when I switch to a 1.5wpg.

I'm guessing the same amount of light intensity hits the HC, so they grew at the same speed. Fert dosing / CO2 remained the same.

I've also noticed that stem plants grow faster when they reached the surface. Higher light intensity nearer to the surface??

2 x 39W T5 bulbs are able to illuminate my tank. But different growth rates between same species of plants are observed.
The plants in corners (a little bit darker) grew a lot slower than those directly below the bulbs.

My light hood can contain 4 x T5 bulbs. I'm considering using more lower wattage bulbs (20W??) so that total wattage is the same while having better light distribution. (I think)

Comments??
We have water pumps to distribute our water around the tank.
Do we have light pumps to move light around?

Regards,
Ryan

This is a tall order for sure. Depth of tank and as bio mass grows the PAR that the plant receive changes drastically. Type of plants, slow grow plants vs fast growth. Also shading of plants has a big factor on PAR.


I looked back on your posts and reminded myself of your light fixture. I would stay at the 2x39W T5 and use the outer most positions (front and back). You have good side-to-side coverage but pretty much centered. It looks like the fixture is about 4" about the water level? This should work OK.


Remember the demand for these will increase as the biomass multiplies(Tom has mentioned many times)


PAR readings at the top of the tank can be very high centered, right-to-left and front-to-back while the top corners can be very low. Raise the light to compensate for this and you loose the punch of light at the bottom levels.


This is a definite result of tank depth and light placement. Tom has always told us to spread the light out This will help reduce low light/PAR areas. Again, biomass shading has a great deal to do with growth rates.


One item of interest, also mentioned by Tom (credit where credit is due), different ballasts do effect light penetration and the life of the bulbs from new and over time.

Chris,

Thanks for your reply once again.

My light fixture is about 2" from the water surface. I lowered it till it rests on the tank, switched on 4 x T5 tubes and moved them nearer to the front, where the HC is.

Tried that for 2 weeks. Observed same growth speed for HC (slow ~~~~) as when I tried 2 x T5 tubes.

All other plants had noticeably increased growth rate from the increased light.

I dose 1.5x EI and keep my drop checker light green to yellow.

Am wondering if I did anything wrong with regards to HC. Been trying to grow HC well since April but to date, I've only managed to stop them from melting / floating. Any advice??

It's tough but I'm not giving up =)

Regards,
Ryan

P.S. I've attached a photo of my tank if it helps.
Thanks in advance!

What about coating the back and sides of the tank with mirrors?

Patience sounds like a better solution.

If it is an academic question, then you need to grow the HC (or the specific species of interest), measure light readings every 2 weeks or so, then vary them treatment to treatment, and say at the end of 12 weeks(or whatever time frame), carefully harvest the plants, rinse off the sediment etc, then dry them at 70C for 48 hours and then take their dry weights per area. The tank, sediment, CO2, flow etc needs be the same, and then you just vary the light in certain defined measured areas.

It's not just using a meter and looking at the plants, you cannot tell that much that way, wet weight and other issues come into play. So dry weights will give you a much more realistic result and reduced the bias errors.


Regards,
Tom Barr