Dale

Hello,
I have a 30gal and 35 gal tank. Both have the same plants, I dose the same fertilizers and amounts, DIY co2, 50% weekly water changes (Barr Method). The only differences are the 30 gal has a fine gravel bottom and 2wpg and the 35gal has fluorite and 2.6 wpg, sometimes 1.7wpg since I leave one of the lights off.
The 30 gal is algae fee and has been for 2 or 3 years. The 35 gal has constant algae problems. The swords in the 35 gal tank have dark patches on the leaves that smells like BGA but does look the same as a previous outbreak of BGA I had about a year ago. The patches, if rubbed will leave a dark residue on your fingers.The swords also have an algae that has the look and feel of velvet.
Am I dealing with BGA or something else. Any reason why one tank has problems and the other tank doesn't?
Thanks for any suggestions.
Dale

HeyPK

if it is soft and slippery, if it has an 'earthy' smell, and if it moves over a period of several days, then it is blue green algae (cyanobacteria)

plantbrain

Two things:
Add more CO2 and KNO3.
Regards,
Tom Barr

Dale

I have 2 bottles of DIY CO2 on the 35gal. tank and only 1 on the 30gal. tank. All 3 are due for a change and I will do it this weekend.
I changed 50% of the water in the 35 gal tank on Wednesday and my NO3 was around 20ppm before the change and 10ppm+ after the change. I did not dose KNO3 since I thought it was getting too high. Should I add more to get it back up to 20?
My K is dosed to get 20ppm, PO4 .6ppm and Fe .1ppm, PH 6.6-6.8 and CO2 usually 20ppm sometimes higher. Like I said before, the 30 gal has been no problem, the 35 always has algae problems.
Thanks for your help.
Dale

plantbrain

Work on CO2 and make sure you dose the KNO3.
It's nothign deep here, just do the work, maintain the CO2 brew often, keep the CO2 at 25-30ppm and check the pH at night before the lights go off to see what the CO2 is.

Swap bottles(use 2 and alternate weeks). Do large weekly water changes, dose nutrient back and then 2-3x during the week.

Regards,
Tom Barr