A picture would help a lot.

Which Flourish? There are many in Seachem's infinite wisdom on naming their product line Flourish as well as their single product Flourish which is a micro fertilizer. Lol!

I'd question the phosphate reading? If just plain Flourish you are only getting P from fish food. Seems like a lot of P from fish food?

And with co2 you should be dosing iron and micros 3x per week every other day. A 50% water change at the end of the week is a must.

Reducing light down to 9.5 hrs tells lights were on way too long. That's more than likely why you are battling algae. That and your Ferts imbalance.

Lastly a kh of 4 might indicate a starting degassed pH of ~7.5. If your lights are strong you may need to be over the often suggested 1.0 pH drop. Many go to a 1.5 pH drop without issues. And if your degassed pH is below 7.5 than your co2 is not enough.

Just my thoughts

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A picture would help a lot.

Which Flourish? There are many in Seachem's infinite wisdom on naming their product line Flourish as well as their single product Flourish which is a micro fertilizer. Lol!

I'd question the phosphate reading? If just plain Flourish you are only getting P from fish food. Seems like a lot of P from fish food?

Just the straight Flourish - the one with the micronutrients.

And with co2 you should be dosing iron and micros 3x per week every other day. A 50% water change at the end of the week is a must

More Iron and Micros, okay got that. . . I'll try and do the water changes more often. As it is, I change 50% when I can (up to an interval of two weeks, but usually about 10 days)

Reducing light down to 9.5 hrs tells lights were on way too long. That's more than likely why you are battling algae. That and your Ferts imbalance.

I'll be rolling back the timers a little more, as I'm sure I'll need to.

Lastly a kh of 4 might indicate a starting degassed pH of ~7.5. If your lights are strong you may need to be over the often suggested 1.0 pH drop. Many go to a 1.5 pH drop without issues. And if your degassed pH is below 7.5 than your co2 is not enough.

Just my thoughts

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I'm not sure I fully get what you are saying. How does the kh tell you about my degassed pH? I would consider my lights to be moderate.
I'll have to check my current degassed pH, but the last time I did, it was a 1.0pH shift.

 

Thanks everyone. I really appreciate the input from everyone who chimed in. Special thanks to Pauld738 for his honesty about his water change schedules and the algae he deals with considering how great those photos are! So many folks on these message boards are doing such an amazing job. I don't often read about less than perfect, punctual routines for upkeep!

Here's the 45gal tank I'm posting about, I took this shot this morning during a feeding frenzy! (Free Columbian Tetras for Adoption!!)
You can see the GSA on the Anubis leaves. Can you see Amazon sword leaves in there? I attribute the disintegration of the leaves by saying "it's an old leaf!" - Truthfully, I have no idea how long the leaves should last, or if I'm showing another nutrient deficiency. (I put a couple of API root tabs in the substrate every month or two)

Needs more pruning! (right side next time!)

 

Nice tank! I love it. But yeah, that's a lot of fish for that size tank.

I'm guessing you will really have to play with your lighting to get that GSA in check.

I'd also try dosing Phosphates. Many on here are at 4ppm. Some go higher, closer to 10. Worst case scenario is you stop dosing it if nothing happens.

It is pretty awesome, though, that your nitrates are as low as they are. I'd say you are not that far off from finding the perfect ratio. Hopefully, lol!

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I have been told and everywhere I have read it says you always should aim for 1PH drop and that has always been my approach..

Not saying you are necessarily wrong buuut...

The 1.0ph drop does not equate to 30ppm co2 concentration, which is actually what is recommended, but rather a 10x increase in your starting co2 concentration.

It used to be thought that most tanks started out with 3ppm co2 due to atmospheric pressure but it has since been shown many times over that there are other factors that affect this. Usually this means that the tank starts out with less co2 then previously thought, which is why many can drop their co2 well beyond the often recommended 1.0ph drop.

Here's a link in case anyone wants to read more. It's from awhile back and a lot is going on with this thread. Tom Barr even makes a cameo so I would assume if any one of the topics being discussed where off he of all people would speak up. Lol!

KH and CO2 levels

Hopefully the link comes thru on my phone.

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GSA is usually too much light,not enough thriving plants + too many fish. Its easy to do in new set ups. Later,it's just not enough plants and too many fish making fertilizer...but it goes down to not really a problem as plants fill in.

 

One more about algae getting out of hand? I forget to always add "Lower the temperature of the water to 73F more or less." At 80 f,and the like,algae just is built for that metabolism to thrive..many plants common in the hobby really do prefer never over 75f for example.

 

What is the ideal minimum Phosphate PPM in a tank? As per Seachem website:
The beginner dose raises phosphorus by 0.05 mg/L (0.15 mg/L phosphate). The ideal phosphate level will vary, but generally ranges from 0.15–1.0 mg/L.

To answer your question, I believe and have always believed the ideal minimum Phosphate PPM in a tank is 1 ppm. However, practical experience has shown me that 2 to 3 ppm PO4 is good for preventing GSA and does not cause too much other algae.