Algae and soil substrates

The last two tanks I've set up with the intent of using plants I've went with the layer of soil under another substrate method a lot of you guys seem to favor.

I admit that the plant growth is great. I've got vals that I'm pretty sure I could have watched grow at first. All of the other plants also started off doing wonderfully. Then I ended up getting tons of algae growth. The soil doesn't mention any sort of manure or compost etc. that would be obvious decaying organic matter. I'm thinking this is just a bit of new tank syndrome, but I've always had it settle down after this much time.


The first tank is a 29 gallon.
This tank has been set up since fall of last year.
It stays right around 60F.
Has a maxijet 1200 flowing across the back of the tank and an Emperor 400 HOB filter running on it.
Inhabitants all of which seem to be doing well are as follows:
1 johnny darter < 3"
2 orangethroat darters ~ 3"
a few ramshorns and various other inverts that may or may not have managed to hide out under the logs and avoid being eaten.

It's planted with anacharis, lots of duckweed, frogbit, and mini water lettuce, a bunch of java fern, java moss, a couple species of vals, and a few different anubias. All had been experiencing great growth until the algae started taking over.

The substrate I used in this one was a cheap top soil about an inch or two deep covered by an inch and a half of eccocomplete.

It gets massive growths of long strand algae, and a bit of cyano in the corner where the maxi-jet doesn't hit. I've treated twice with peroxide and it did the trick, but it also beat up my vals. A few weeks later the algae comes right back. Water quality seems fine, which isn't surprising given the massive algae growth.


The other tank is ~40 gallon filled to about 15 gallons.
This tank has only been set up a few months now.
It is heated to upper 70's
Has very low flow, and is filtered by a large hydor sponge filter.

The inhabitants are:
1 young of year stripe neck musk
A few ramshorns and scuds if the turtle hasn't caught them yet.

It's planted with some java fern, a crinum onion, a bunch of anacharis, a bunch of mini water lettuce and frogsbit, and a bit of java moss that is quickly being cyanoed out of existence.

The substrate here was the same top soil used in other, except this time I ran it through a fine strainer and removed all the chunks of rocks and sticks out. I then covered it with about 2-3 inches of fine sand.

This tank has a lot fewer plants rooted into the soil, but the ones it has were growing great before the cyano took over. I'm assuming adding a powerhead will clear most of it up, but it is relatively easy to remove from the sand and the turtle seems to enjoy the placid waters. So I've just been dealing with it.

I'm just a bit curious if everyone else has this problem with soil substrate tanks or if I'm making some fatal flaw. I've not had this much of an algae issue with any other tank I've had. The tanks seem very lightly stocked to me, and while I feed fairly heavily given the limited populations it doesn't seem like it should cause this sort of algae growth based on previous experiences and other tanks getting the same treatment with different substrates.

Edited by Clayton, 27 April 2009 - 03:31 PM.

I have several tanks with soil/sand substrates. When they are first set up, I get a ton of algae. Things look really awful for a while, then after the plants get going the algae gradually goes away. I've never used Eco-Complete. In my tanks, soil is used instead of the expensive store-bought substrates.

How long have your tanks been set up?

Sorry looks like I was editing as you were typing. I added in when the tanks were set up. The 29 has been up since the fall. I think I set it up Sept-ish and added the fish in late October. The turtle tank is fairly new. I can look up the exact date I set it up, but off the top of my head its only 2 or 3 months old.

In all honesty I can't say how ecocomplete does with plants on its own. I really only used it in the 29 as I like the way it looks. It has a very nice color and is really variable in grain size with a lot of it being almost sand up to decent sized chunks of gravel.

I've got a 120 that it is the only substrate in. I've never had an algae issue in that tank, but anything that I plant the red eared slider mauls within a couple of days. The tank gets almost no algae growth despite having a pretty sizable bioload and getting lots of heavy feedings. It has a LOT of filtration running on it, but that still doesn't do much for the nitrates.

Do you have any other planted tanks that get the same amount of lighting as the soil tanks? (Maybe you've said it above and I missed it.). Whenever algae persists this long, I am suspicious of phosphorus in the water. Do you use public water? Many municipalities add phosphorus as a corrosion control agent, and when well lit, grows algae like gangbusters (espeicialy cyanobacteria in my experience). When I lived in Georgia, I had to use a DI filter to get the phosphorus out. If you are on public water, you can call the water department and ask them if they add phosphorus (make sure you talk to someone who really understands how the water is treated, not just the person who answers the phone). If so, you can try those phosphorus-removing granules to see if that has an effect. Note that some water sources also have higher phosphorus levels without the water department adding more, especially if the intakes are downstream from wastewater treatment plants).

My thought here is that with higher lighting, the phosphorus can be used by the algae. With lower lighting, light becomes the limiting factor, so nutrient content isn't as important.

Other possibility is that the source of the top soil had a high nutrient load. (For example, maybe from a farm field that was recently sludged, then sold for subdivision development, during which the topsoil is often stripped and sold.) It's possible, since such topsoil isn't tested for nutrients. I suppose you could take a bit of it and send it to your local extension service for nutrient analysis (for a minor fee; used to be free).

I know you said you had duckweed and frogbit - I would keep up with the frogbit and harvest when it starts cutting the light your other plants need. It's a great nutrient remover. Don't harvest too fast - you want lots of them in there to multiply.

In a nutshell, I'll bet that phosphorus is your problem, not nitrogen. If nitrogen does come out high, though, you can encourage denitrification by jamming some organic material with a high carbon:nitrogen ratio under the sediment. For example, maybe take some sawdust, freeze in ice cube trays with water to make little blocks, and stick them under. Heck, I've even used cubes of sugar (lots of carbon there!). Note - I have never tested this method scientifically, but I do know a lot about the nitrogen cycle in natural systems - the more carbon in an anoxic zone, the more nitrogen is removed.

Good luck, and try not to get too frustrated. Do call the water department. Let us know what you find out. We'll go from there.

Note - I have never tested this method scientifically, but I do know a lot about the nitrogen cycle in natural systems - the more carbon in an anoxic zone, the more nitrogen is removed.

Could one simply add carbon for a filter to the soil?

Thanks for the advise.

I'll test the phosphates(I'm guessing the two are related) when I get home. I'll call the water company and ask about phosphorous. Are there any other names or buzzwords I should be looking for in regards to it? If that doesn't pan out I'll send off a bit of the soil and see about getting it tested.

As far as similar tanks go these are the first two tanks that are actually planted in this house. They were set up differently at other times, but also in a different town. So it doesn't offer much any sort of control for the water.

In my town, I can call the water department and ask for a chemist. They can answer questions about phosphorus. If yours are like ours, you have to know what to ask, since they aren't real chatty.

What you want to ask is "Do you add any phosphorus-based compounds for corrosion control?" If the answer is no, ask if they have tested their water for phosphorus. You can explain that you are trying to better understand your water's chemistry for use in a fish tank.

Well it looks like there are no phosphorous based chemicals used in my tap water. The woman I spoke to from the water company was very friendly though, and apparently they do a bunch of free testing as well. So I should be getting a kit to take some samples and send back to them soon.

I tested the tanks along with my tap for phosphates. One tank was hard to tell since the water is pretty tannin stained, but it couldn't have been higher than 0.5 ppm. The 29 gallon was at ~ 0.5ppm. The tap water didn't show any noticeable levels on my test kit. So it looks like if phosphates are the issue they're probably not coming in with the water. The various frozen foods are likely providing more than enough for the algae, but I've got a skinny darter that makes cutting those back not really an option.

I might try some phosphate removal media and see if that gets me anywhere.