Thread algae woes. Thread algae understood?

An old nemesis found

In my last post I mentioned that I’ve been fighting algae for the last six months. That is true. And before my long dry-spell of no posting, I mentioned that I though I had conquered the persistent GDA on the tank walls, that I had been fighting pretty much since the tank went up.

But after declaring victory, I realized that I had been cheating.

Normally I don’t do regular, manual water changes on my tank. The automation on the tank does multiple small drain/fill cycles each night that equates to a 50% water change every three days.  But while I was fighting this algae on my glass, I had been doing a 90% water change every weekend. This allowed me to clean my glass of the algae. And over time, the amount I was cleaning every week became less and less. Until finally I thought I had it licked. But all that changed when I decided to go back to my normal routine of no huge weekend water changes with rigorous glass cleaning. And WOW, the algae came back in a hurry.

And rather than aggressively scrape it off, I decided to let it go a few weeks to see if this really was GDA (green dust algae) as I thought. It virtually brushed off, easy to clean. So I thought I knew what I was dealing with. But I was wrong. After a few weeks of letting it grow, the acrylic tank walls were covered in beautiful green threads, waving in the current. Thread Algae! My own personal algae nemesis returned! Or rather, had never really gone away.

In the Scolley’s Follies category here you’ll see a tank that got badly infested with this stuff. And I mean bad. There were extenuating circumstances in that tank that you can read about in that post, but bottom line was - thread algae was completely out of control in that tank. And now I found out that it is what I had actually been fighting in this tank for a year and a half. Why? Or rather, why my tanks?

I had a very long thread where I battled this stuff in detail, aggressively for months, documented over at plantedtank.net. So I went back and re-read that. And then I started researching other places where I found this algae. And I found it to be a bad nuisance algae in another type of tank - marine tanks. Granted, I’m sure it’s somewhat different on some technical biological level. But fundamentally it looks the same. And everywhere you find this stuff, there are a few things in common, beside the obvious light and water. They are:

1. Strong water current
2. Phosphate
3. Silicates

Strong water current

This seems obvious. Just look at the algae’s morphology. It is long threads, that grow by adding length to the thread - threads that wave in the current, picking up nutrients as they pass by, and growing the thread. You don’t find this stuff in slow or still waters.

Phosphates

I battled this documented in dialogues with well intentioned “experts” over at plantedtank.net. There is a popular belief that by making sure that you have enough of every nutrient your plants need in your tank, then your plants will flourish, and they will somehow magically “out compete” algae, even though there is enough nutrients to go around for both plants and algae. Well that’s bunk. Unfortunately a large vocal group in the planted tank community drinks this particular kool-ade. Not me. I’ve proved it to be incorrect to my own satisfaction, in my own tanks.

It is clear, that if you run out of any given nutrient, opportunistic algaes will take over. So you can’t bottom out of any nutrient. Zero ppm is bad, even for phosphate (in a freshwater planted tank that is). And it is true that your plants flourish in an excess of nutrients. But where the wheel falls off the wagon with this thinking is the belief that flourishing plants will make your algae problems go away. In some tank it will. But in others not. If you, like me, have one of those nasty algaes that will not die while your plants are flourishing, you’ve got to deprive the algae. Or find something that eats it. And for me, in this tank, that has meant managing my phosphate level so that it remains between 0.05 and 0.2 ppm. It’s seems to be enough for the plants, and it appears to seriously limit the growth of the thread algae.

Silicates

This is the real key. I’m not going to say that you won’t find this algae in tanks without silicates present, but you sure as heck will find it in abundance in plenty of tanks with excess silicates. Want to see an example? Just go to your nearest pet shop and look for it in the marine tanks. Chances are very high that you will find in in tanks with silica sand bottoms, but not in tanks with bare bottoms or calcium substrates. And I’ve never had it in a tank that did not have sand on the bottom either. But I’ve got more evidence, and I find this somewhat compelling…

When I was battling this the first time - in my original Big Clear Kahuna tank - it was my first tank with a sand substrate. And because I was doing everything “right” in conventional planted tank wisdom, I eventually questioned my test values of my water, and sent three samples off to be professionally ($$$) tested. One sample was my tap water. One sample was from my Big Clear Kahuna tank that had the awful thread algae problem. And one was from my little “Mickey’s 20″ tank that had no thread algae at all. In fact I was barely ever even doing water changes in that tank, because it was so stable. That should have been a clue. The test results can be found in the chart at the top of this post.

At the time I was focused on my NPK values, and to some extent micros like iron and magnesium. But I was foolish to ignore the silicate readings. They are unusually high for, and they tell a good story. The silicates in my tap water is a very high 7 ppm. They were half that in the Big Clear Kahuna, and were less than 1 in Mickey’s 20g. I can’t explain why it’s so high in my tap water. I gather that some water companies actually add silicates for some “benign” reason. But that number plummets to less than 1 in Mickey’s 20. Why? Because plants (and algae) do use silicates. And with very infrequent water changes, even the very high starting point of 7 ppm got cut down to residual levels over time by being consumed by plants. But the Big Clear Kahuna on the other hand was receiving weekly 50% water changes, which should have boosted the silicates, keeping it up at a near 7 ppm level. And keep in mind, plenty of silicates were also available due to the sand substrate. So why were the silicate being knocked down to 3.5 ppm, when my plants were barely growing they were so covered with algae. What was reducing the ppm from 7 to 3.5? Easy! The algae itself was a major silicate consumer. And the abundance of it - combined with plenty of phosphates and nice brisk water flow - was enough to kick that particular algae into overdrive.

So high water is important. And the presence of phosphates is too. But in my opinion the lynch pin is that excess of silicates. That explains why so many people have “proved” that this is not caused by excess phosphates. It’s not. It’s caused by the combination of all three things; flow, phosphate, and silicates. Remove one and it goes away.

My current problem explained

So, if silicates are so important, why was my current tank getting better - as evidenced by less algae on the tank walls - when the tank remains bathed in excess silicates? Between the sand substrate provide substantial silicates, and the tank is automatically providing itself a 50% water change every three days (of 7 ppm tap water), silicates should  ALWAYS be there in excess. But I’m managing the phosphate level now. As stated before, I’m keeping it between 0.05 and 0.2 ppm, and the algae is staying in check. And the plants are growing.

Unfortunately this means I’m having to do water testing - which I hate - and periodically adding Potassium Phosphate - which I also hate. And all this may get messed up in the spring, when my tap water begins to get influenced by agricultural runoff, and the Phosphate ppm starts to climb. I may have to resort to installing an DI filter. I hope not.

Concluding

All this is my own conjecture, based on my observations. The test here is going to be time. Will my tank thrive, and remain relatively free of thread algae now that I’m keeping my phosphates low?

Here’s a pic of the tank now, so you can get a before and after view. Here’s “before”. You can see the evidence of where the algae was on every leaf, and can even be found in some clumps of moss if you zoom in. And finally, the Hygrophilia corymbosa got whacked back pretty bad. Lets’ see if it can bounce back without me doing the weekly algae cleaning, and tightly managing that phosphate level. Time will tell.