Here's a question for you more experienced folks....
I've got a planted freshwater aquarium that's been running for about 4 months now. 4 Watts/gal broad spectrum power compact lighting, CO2 injection to 15ppm, GH & KH both @ 7dH. Temp @ 80F
In the beginning, I went through several different kinds of algae outbreaks. The last of which was a big outbreak of hair algae. I ran the filter with some Phos-guard in it and the hair algae disappeared almost overnight.
During that time and until recently, the plants had been growing like crazy and all the fish were happy (fish still are happy). I was left with a fairly manageable infestation of green algae growing on the glass. I had to scrape it off about every two days to keep the glass looking clean.
Being a lazy person, I thought I might reduce the glass cleaning if I could reduce the nitrate level. I bought a nice, used "batch" denitrator from a friend. This unit uses an ORP probe to measure the redox level in the denitrator box. When the level drops below the preset, a pump comes on and puts fresh aquarium water in the denitrator box, allowing the nitrate poor water to run back into the tank via an overflow. It takes about 6 weeks to culture the bacteria in the denitrator. During the "break in" period, you lower the "trigger" point on the ORP controller weekly to make the water in the box get more and more oxygen poor before it gets pumped back into the aquarium. The denitrator box contains bio-balls for the bacteria to grow on and some things called "nutra spheres" that supposedly help feed the bacteria.
To make a long story short, everything was going well until the denitrator was almost completely "broken in." During the last week of the process, the green algae growth diminished significantly. However, the hair algae has come back with a vengence!
Further, although the Wisteria and most of the other plants in the tank still look okay, the Amazon Sword plants are developing brown, dead areas on their leaves. None of the plants seem to be producing oxygen bubbles at the rate they used to, even though the CO2 concentration remains at about 15 ppm and I've maintained the same daily and water change fertilizer / micronutrient doses I've always used with such good results.
I have a nitrate test kit whose first color change occurs at 20 ppm. It reads "zero" which I interpret to mean something between 0-20 ppm.
I stopped using Phos-guard after initially reducing the phosphate levels for two reasons-- 1) I'm told that nitrobacter/nitrosomonas need a small amount of phosphate to do their ammonia -> nitrite-> nitrate job; and 2) I figured changing 20% of the water twice a week would keep the phosphate levels in check. It seemed to be working.
My question is... what made the hair algae come back when the nitrate levels dropped? -and- Is this related to the unhappy Amazon Sword plants and the reduced production of oxygen bubbles when the lights are on?
I have thought of several possibilities but don't know which, if any, is the likely culprit. Things I've thought of:
1. Reduced nitrate has stopped the higher plants from taking up phosphate, letting phosphate levels rise and the hair algae have capitalized on that.
2. There is something in the "nutra-spheres" (in the denitrator box) that is feeding the hair algae. Unrelated to phosphate levels.
3. It was never the higher plants that were keeping the phosphate levels under control, it was the green algae. When I starved it of nitrate, the green algae stopped growing and consuming phosphate and the hair algae took advantage.
And with reference to the dead spots on the Amazon Sword plants....
1. The Amazon Swords are unhappy because of the low nitrate levels.
2. They are unhappy because the nutrients in the substrate have become depleted and the timing is coincidence.
(The leaves on the other plants (Wisteria, Moneywort, Crypts) all still look fine)
Do any of you folks think any of the above seems the likely culprit? Anything else that I haven't mentioned that you think could be responsible?
What should I try first?
thanks and Happy Holidays...