I have a 72x18x23 135 gallon.
Lights— 2 Finnex Ray-2 dual 7,000K
2 25 Watt T8 fluorescent bulbs.
Light schedule -- T8's are on from 9am to 10:30pm. The Finnex are on for 5 hours a day—divided into two different 2.5 hour intervals.
Substrate—Sand
Ferts -- None.
Plants--Jungle Val all along the back glass and on both ends, java fern all died or just stayed tiny, pothos in the back corners of the tank lids
Water -- PH is 7.8, temp is 80, ammonia=0, nitrite=0, nitrate=10-40
Fish-- 15 Vieja, about 3 inches long, 3 other bigger CA Cichlids. 5 Clown loaches. So, lots of fish in this tank
If I turn the Finnex lights on for a full 6-8 hour cycle, algae covers all the leaves on the plants, the rocks, the glass, etc. If I turn the Finnex off the algae calms down, but the plants don’t do well. Do I raise the Finnex lights higher to lessen the light and run full 6 hours with the grow lights? I try to wipe algae off the Valisneria leaves, but that’s futile. It just grows right back and covers the leaves. What would happen if I just trimmed all the Val plants’ leaves that have algae? I notice that some very long and healthy Val leaves don’t have algae at all? What’s that about? I've heard a lot about "balancing" nutrients and light, but I have no clue what that's all about. So what do I do with this tank?
Glad to see you made a thread here
Now, onto your tank. Are the two T8 fixtures side by side or are they the full length of the tank? That will make a difference (although only slightly) in your lighting intensity.
I'm going to assume for this post that you have 1 t8 in front of 1 led on both sides of your tank. Now you are running the t8's for 13 hours....which is a lot. I would cut your lighting time wayyyy down, something like 8-10 hours, 10 being on the long side tbh. If you don't already have timers, get timers...its very much worth it.
Now, the LED's is where you run into a bit of a problem. Your tank I assume is 23 high right? And the length of each fixture is 36? That should put you at about 40'ish PAR from the LED's alone, which is by itself on the high end of medium light.
What does this mean for you? Well, you are at very high medium light, without dosing any fertilizers. Algae is able to use up nutrients faster than plants, and require less of certain nutrients that plants need in order to grow. As I see it, you have two options for avoiding algae currently.
1) Raise your LED lights even higher from the top of the tank. Problem with that is then your T8 fixtures will physically be blocking some of the light from your finnex, meaning you may have to raise those as well, which would prove your T8 fixtures ineffective at a higher height.
2) Start dosing fertilizers. As you are now, you could stand to lessen your lighting output a little by just using something to block a little light (as others have suggested) or raising the light. But for this option you don't need to raise them all that much, and you can make use of your medium strength lighting. For a tank your size, I would learn how to properly dose EI dry, as that is the most cost effective method. You have no nutrients in your substrate anyways, and I feel going to low light would only slow down how much longer you can stave plants for of nutrients. Fish food and poop will not have everything plants need in it. I suggest EI over other methods because I assume you are already doing at least 50% water changes weekly with this tank given its stocking, and EI fits in perfectly with that idea. Your plants would grow significantly better this way as well, and faster than if you did option 1.
I don't recommend using floating plants to block the light btw, at least not so far as option 1 is concerned. Relying on floating plants when you have too much light tends to not go over well, as your lighting intensity will vary greatly with the removal or growth of floating plants. If you did option 2 though I think floating plants would work well, as they would appreciate the nutrients. Only thing is they aren't the biggest fans of a lot of water movement on the surface and flow, and I don't know how your tank is in that regard.
All planted tanks run a balance of 3 factors, lighting, nutrients, and carbon. Here is a quick breakdown of what that means for the three levels of lighting
low lighting: minimal nutrients (weekly nutritious substrates/fish waste): minimal carbon (what is naturally in the water/carbon additives)
medium lighting: increased nutrients (depends on how close to low or high light): increased carbon (carbon additives useful/injected co2)
high lighting: high nutrient content (daily dosing of some kind, or incredibly rich substrate but may only last a year or less before needing additives): pressurized co2 required (might be able to get away with paintball co2 on a smaller aquarium but not as reliable)
If you went to the low light area with this tank, since your substrate is inert sand, your fish poop could only do so much and I would recommend that you look into dosing liquid PPS-Pro like LS2012 does. Medium light you might be able to still do liquid PPS-Pro but I personally prefer EI dosing, although modified to accommodate for no pressurized co2.
I'm also not going to recommend co2 injection to you, because given your stock and plant list I feel that might not be something you want to spend on. If you decided in the future you wanted to go that route though you are more than welcome to, but personally for this tank I wouldn't, not until the plant mass was significantly increased anyways.