algae and co2

[Gonjinn]

hi all,
i'll try to keep it short!
heavily planted hi-tech tank, 100% ro water, gh 5, kh 9, EL ferts, .
problem is, i noticed green algae was spreading quite quickly over everything and, more recently, BBA has appeared in hi flow areas.
the tank ph sits naturally at around 7.1 which, by chart, is in the sweet spot for co2 but that also means that for a while the regulator has released virtually no co2 at all.
i know i should set my ph so co2 will make it drop by 1 point but that would increase my kh too and i'm at 9 already so i'm a bit worried to keep pushing.
in adition to that, i realised the other day my nitrate crept up to 60-80, so i'm cutting on macros and doing more water changes but i'm not sure just lowering them will sort the algae issue.
any suggestion appreciated.

thanks!

 

[ZxC]

Wow... You've got all the "right" information, you aren't applying it correctly resulting in your algae

100% RO water means 0 gH and 0 kH and ~ 7 pH. How are you testing this? Are you gH and kH boosting?

Just because your pH is around 7, does not mean your CO2 is at adequate levels. If your regulator isn't allowing a bunch of CO2 to enter the tank, you are certainly not getting enough CO2.

Insufficient CO2, and inconsistent dosing / water changes is where your problems are.

 

[Gonjinn]

hi, thanks for your reply.

yes, i'm remineralising my water. i keep my gh at 5 and use an alkaline buffer.
i have control over all water parameters and my initial goal was to raise ph to 7.8 in order for the co2 to keep it down at 6.8. problem doing so is my kh raised too in doing that so lowering ph to 6.8 would be out of balance with the recommended value for KH 9 ( which is what i have at the moment).

that's why i feel a bit stuck!
if i raise ph to get the co2 pumping, then KH is going to raise too and keep chasing it can only end in disaster.
if i don't raise the ph, then the water sits at 7.1 and that would mean co2 would notbe released.
if i set the regulator to keep the ph down to, say, 6.1, then i would have co2 distribution but, according to the chart, i would end in the red zone quite badly.
it would be in the red even if i set it at 6.8 and that would not release a lot of co2 anyway...

 

[Gonjinn]

must add, i keep a very regular maintenance schedule. 50% wc once a week, ferts dosing daily with the EL method and filter cleaning once a month.
i try and keep everything by the book but something's off and cannot point my finger at it :/

 

[ZxC]

Okay... You've been mislead unfortunately.

The kH / pH / CO2 chart is not accurate, it is for reference only.

Who gave you a recommendation of a kH of 9? That is insanely high for a planted tank using 100% RO water..

Aim for 0.5 - 1.0 degrees of kH. Plants prefer super soft water, and a kH of 0.5 - 1.0 is more than enough to keep pH stable.

That will give you a pH of around 7.1 - 7.2, then set your controller to drop pH to 5.9-6.1 or so. Then you will have enough CO2, plants will prefer the soft water, and you don't have to use truck loads of buffer. Use KHCO3 for the kH buffer... and use CaSO4 and MgSO4 for the gH buffer.... 3 parts Ca to 1 part Mg.

https://rotalabutterfly.com/nutrient-calculator.php is the website to use so you can dose the correct amounts. Dose gH and kH booster into the water change water prior to adding it to the tank.

Target 30ppm Ca and 10ppm Mg and 1 degree of kH to start.

 

[ZxC]

must add, i keep a very regular maintenance schedule. 50% wc once a week, ferts dosing daily with the EL method and filter cleaning once a month.
i try and keep everything by the book but something's off and cannot point my finger at it :/

EL or EI?

Never heard of EL dosing.....

 

[Gonjinn]

ei, sorry