Diatoms (Brown algae for months)

[the loach]

The first step is really to order a KH test, you will need this. There are other ways to lower pH, like CO2 injection. Flourish Excel is "liquid" CO2 which is not very effective, as you have seen. I doubt that your tap water is acidic and hard. Leave it sitting for a day and then test pH.
Also do not confuse GH and KH. Chances are your water has a low KH which causes pH swings. We need readings on both tap and aquarium water.
1200 Lumens is good for 10 gallons but "white" and "blue" leds are laughable as a specification. Still focus on getting the pH down first.

 

[Jah410]

Okay, I'll try to get the pH down and look into ordering a kH test. Just to confirm what else I should be doing right now.

You said I should half my water lettuce to keep a higher nitrate level for other plants as well? Should I am for like 10ppm?

Also, should I forgo use of any fertilizer right now until the pH is lowered closer to 7?

 

[fishorama]

I don't use LEDs but 8-12 hours is a long time. I do 6-8 hours with T-5s. I agree with much of what TL said in regards to GH, KH etc. Until you test, you can't know. Excess ferts can add to your problem. In my medium-highly planted tanks I rarely see nitrate of 5ppm, usually less.

 

[the loach]

Yes for now remove at least half of the water lettuce. You need some nitrate in there and you have a lightly stocked planted tank so it's not a bad thing its in your tap water. Eventually you will have to do without any water lettuce. Fertilizing is just feeding the algae at this point since your plants are CO2 starved.
It's possible to have a poor spectrum light so it favors algae growth but the duration itself isn't the sole cause for algae growth. I don't like dark tanks to look at so I have all of the lights on for 12 to 13 hours a day... no algae to speak of.

 

[Jah410]

Okay great! I ordered a gh and kH test that should be here tomorrow so I'll update you with those parameters when it gets here.

Rn my pH for my tap is 7.0 when not run through the water softener. I'm currently filtering it through phosguard, but will probably wait for the gH and kH readings before I add to the tank. If they are unfavorable, I can consider the peat, or perhaps mixing with some RO water.

 

[Jah410]

The first step is really to order a KH test, you will need this. There are other ways to lower pH, like CO2 injection. Flourish Excel is "liquid" CO2 which is not very effective, as you have seen. I doubt that your tap water is acidic and hard. Leave it sitting for a day and then test pH.
Also do not confuse GH and KH. Chances are your water has a low KH which causes pH swings. We need readings on both tap and aquarium water.
1200 Lumens is good for 10 gallons but "white" and "blue" leds are laughable as a specification. Still focus on getting the pH down first.

Okay here are the test results (pH is for degassed water)

Aquarium = tap: pH=8.0 kH=8 GH=1-2 Nitrate<5ppm
Hose (non softened tap): pH= 8.0 kH=4 GH= 2-3 Nitrate=15-25ppm

So what does that tell me? Should I switch to using the hose water? Or perhaps a mixture? I find it odd that the pH of the tap raises from 7-8 when it has a decently high kH... It must have a lot of CO2 in the water.

 

[Jah410]

Gonna amend the hose water: KH= 3 so I should probably use a combination of hose and tap water to get closer to around a 6...

 

[the loach]

It is not completely clear to me what you mean with hose and tap and aquarium water...
As I see it now you have substrate or rocks in your aquarium that increases KH and pH.

To test the pH from the tap (or hose?) put the water in a glass and test the next day. KH won't change but pH can.
Your "hose" water is just fine for an aquarium. Lower the spray bar from the filter so it is under water... test the next day this can help to bring the pH down a bit in certain circumstances. If you have an air pump disable it as well...
Don't clean the filter as much, more detritus in the filter will over time also bring the pH down a bit.
Your "hose" water is soft enough, no need to change that.

 

[Jah410]

I have a water system that softens our water (GH via ion exchange), and stabilizes our pH via sodium bicarbonate (I think). The water that runs through this system I'm calling tap water. It has a higher KH because of the Sodium bicarbonate KH= 8-9 and a lower GH because of the ion exchange.

The hose does not run through the system as it does not need all this balancing for the yard so the KH is lower through the hose. Interesting, the pH is basically the same after degassing both the hose, and the tap water. The hose may be slightly lower (7.8) while the tap is slightly higher due to the increased KH I assume (8.0-8.2).

Up until now, I have been using the tap water in the aquarium (not the hose water) which is why I just said aquarium = tap. Sorry for the confusion!!!

So I'm adding the hose water to the aquarium now and it has been run through phosguard to remove any potential silicates. The KH in the aquarium should be about 5-6 when I am finished with it. I have also scrubbed off a bit of the algae buildup on the plant leaves and siphoned out a decent amount of water. I've also removed about half the water lettuce in order to maintain a more stable nitrate level of 10-20ppm between water changes. I've stopped adding Thrive in the meantime as well. Finally, I have reduced my lighting down from 10 to 6 hours. I know you said that lighting duration did not seem to affect algae, but I'm finding that the longer the lights are on, the more algae is growing. I can try what you mentioned above about lowering the pH.

Do you have any other suggestions/ changes you would make from what I have described above?

 

[the loach]

Ok, so your water system "softens" the water from GH2 to 3 to GH1 to 2?
There is no need for that in your aquarium, your water is already soft. So I would just use hose water. A higher pH will only make it much harder to get it down.... do water changes until the KH in your aquarium is ±4.
If it gets up again... you will need to remove rocks or substrate.

Lighting duration does affect algae growth... but it is not the sole cause. When you provide proper conditions for the plants a longer photo period will not cause more algae. Just reduce lighting until you get the pH down.
Lower the spray bar so there is no surface agitation. Keep track of the pH and note to always measure at the same time of day, it is normal for the pH to be higher before the lights go out and lower when they come on. You can use some peat or catappa leaves to lower the pH faster. Remember it is not just getting rid of the algae it is getting to tip the balance in favor of the plants (for which reducing light will do nothing).
Provide the right conditions and the plants will outcompete the algae.