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Lighting time and intensity in lowish tech


25 Aug 2017
I’ve been pondering if more light over fewer hours is different to less light over more hours from algae point of view. It seems like it would be reasonably easy to calculate how much longer you can keep lights on if you reduced intensity but I suspect it isn’t quite that straight forward. Any thoughts on this are appreciated.

As context, my angelfish are breeding and do look after their eggs well when lights are on. During light off period them or someone else eat eggs and I’d like to be able to leave the eggs with the parents at least until they hatch so have increased photoperiod. All my plants are undemanding but I do add EI-ferts and EasyCarbon daily. Majority of plants that survived for any length of time seems grow well. However I recently seen signs of Cyanobacteria, green algae both in filamentous form and dots on glass and relate this to extended photo period. I do appreciate that some of that may relate to bioload and flow patterns but it’s difficult to separate what comes from where.
Can you give us some more info. Pics of the tank and algae and details about your light, its make, light intensity and photoperiod, tank dimensions, filter output etc would help.
I’m not necessarily after trouble shooting of my own tank as such but more general discussion of people’s thoughts on algae growth in relation to light intensity and photoperiod.

Obviously if I can sort out my own tank with little trial and error then that’s a bonus!

Fluval Osaka 260 (this is a deep tank at 70cm)
Fluval 305 filter with coarse and medium foam, biomax rings and Purigen. Spray bars from back towards front glass
Hydor Koralia nano circulation pump attached to the side of the tank 1/3 of the bottom up to increase circulation behind large bog wood pieces
Temperature set to 25 degrees C
Lights are two sets of T5HO light fittings with first set about 15cm above water surface with Arcadia LED 12W and T5HO grow bulb 39W and second about 23cm above water surface with two T5HO grow bulbs. All T5HO are about 18months old and probably could do with replacement
Substrate is Fluorite black
Daily EI- ferts with recommended dose according to manufacturerAquarium plant food uk
EasyCarbon 15ml per day which is about 3x recommended dose
The tank is fairly highly stocked with 5 angelfish, 5 rams, 8 bronze corys, 5 otos, 10 neon tetras and 4 rainbow emperor tetras
I don’t test water very often but ammonia and nitrites come as 0 mg/L and nitrate <5mg/L

I get some green algae on glass and on java ferns

Cyanobacteria and diatoms on plants on the bottom
Hi all,
more light over fewer hours is different to less light over more hours from algae point of view.
I'd go with a reasonably bright for a short photo-period (but I definitely wouldn't go under six hours) and then a dim light for the other 18 hours.

If you just think about all the photosynthetic organisms as "plants", and don't differentiate between "algae" (the plants you don't want) and "aquarium plants" (the plants you do want), then all plants need to reach their <"light compensation point"> (LCP) before they can grow.

Some plants need everything <"turned up to 11">, other will have a much lower LCP.

We don't know what the LCP is for most plants, but in a dark room we percieve it as quite a bright light won't reach compensation point and this is even for red algae (like BBA), mosses, Anubias and ferns, which we think have low LCP values.
As context, my angelfish are breeding and do look after their eggs well when lights are on
Have you got an ordinary standard (or table lamp or similar?) you could put near the tank? You can just put a low wattage bulb in it, on a timer and it should give your Angels enough light.

I used to use an old kiddies night light.

cheers Darrel
Thanks! I put on dimmer lighting for majority of the day and 6h on full set. Hopefully this is not going to be a long term problem as there were only few eggs left and I scooped them off to a hang of the side fry tank. I’m not holding my breath to have any left by the time they start even eating anything. On a brighter side I can reduce photoperiod and do a proper cleanup without harassing the fish and being endlessly attacked
I think low light and 6h full blast has been ok with algae issues although I’ve removed some every day. That is brilliant news as another set of eggs has been laid so I’ll have to keep at it. Apparently this male angel isn’t massively keen to this pair concept as he laid eggs 6 days ago with another female
Weirdly I was pondering the same thing just last night. Did some googling and this is basically what I found...

Intensity and duration are not interchangeable.

Some plants won’t start photosynthesis until the light reaches a certain intensity - high light plants. Low light plants will start photosynthesis at much lower light intensities.

All plants need the light to be at their minimum intensity for a certain amount of time to photosynthesise. How long they can grow for depends on the plant variety. This is mostly an unknown number. Although, 5-6 hours is widely considered the minimum amount of time the lights should be left on, and 12-15 the maximum.

Obviously, increasing either light intensity or duration will also increase the demand for the other things plants need to grow, nutrients & CO2. So if light intensity or duration increase, it’s wise to increase the other two too.

I’m no expert, so hopefully I’ve understood my research correctly last night and am not spreading false information - happy to be corrected if I am wrong

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