Chronic Blue-Green Algae

Sounds like you are treating the symptoms but not the cause.

In order to beat the turqoise monster you'll need to balance the tank. I've had a little of this stuff in my tanks before. I fixed what I was doing and after a water change it was gone.

So list out the full details.

Plants: species and numbers.
Stocking: same thing
Fertilizers used:
CO2 type injection method and amont in tank:
Lighting (take a picture). The type of reflector matters a lot.

Can you show us a picture of the BGA and what brand of E.M. did you use, did you check for expiration date? BGA does like light, so if you can minimize the daylight hitting the tank that might help. It's a bacteria so cross contamination is something to consider. I had a bad case of it and was finally able to get rid of it with slightly overdosed E.M. from API. I actually repeated it after a week. It came back after 2 months when I added some new plants and 1 treatment of E.M. got rid of it and has been ok for about a month. Interestingly my BGA was always on the substrate (PFS) and not much else. Prior to treatment, I sucked it all out (comes out in sheets!) then added E.M.

I have used peroxide with a syringe to target algae (2ml per gal.) but as "The V" stated it does identify the cause. Do you test your water No3 and Po4 levels or are using a fertz like EI? Water circulation for dead spots? (my green algae problem got better once I improve circulation and added a little KNo3 since my city water had enough Po4 and I was over feeding live food to my GBR breeding tank.)

The advice of other members about dealing with the source is the only way to handle cyanobacteria. This bacteria (not an algae as someone mentioned) is caused by one thing, and that is high organics. I have seven tanks running, and have seen it only in one of them, sporadically. But any method such as reducing light or blackouts, dosing antibiotics, etc are only temporary, as indeed you have seen. The organics must be dealt with.

More data on the tank will help us. How many fish, and what species? How often are water changes performed, and what volume of the tank? How often are fish fed? What is the nitrate level? And the pH? Plant fertilizers are also part of the equation, though you said you stopped them when you removed the plants.

About two years ago I got cyano in my 70g. I did weekly water changes of just over half the tank (I regularly do 50% WC anyway), removing as much as I could each time. I vacuumed into the fine gravel substrate more than normally I would. I stopped adding liquid fertilizer. It took three to four months of this before it suddenly dissipated and didn't come back. A couple months later it did, so same process. Cleared up again.

While antibiotics will kill this, short-term, this is really not advisable. Antibiotics also affect fish and bacteria, and some plants. I did try this once, and my chain swords all died. It is best not to add antibiotics to a fish tank except to deal with a specific fish bacterial issue.

Byron.

That data helps, thanks. Now, what is the nitrate test reading? And the pH?

With all this data, my thinking is that the nutrient dosing was beyond the needs of the plants, and this will feed cyano or algae. I think I mentioned a relationship I saw between cyano and liquid fertilizer in my tank. I can't say if the levels you were adding of those ferts was or wasn't correct, since I do not maintain high-tech systems and these are quite different from the low-tech or natural methods. But I will suggest that the plants mentioned (numbers and species) should not need a lot of nutrients, so this seems probable. Keep in mind too that these plants will not make a great deal of use of the enriched substrate, and as the cyano has been on the substrate (if I read you correctly) this is another source. There may also have been an abundance of light, beyond what the plants could fully use. And ambient daylight in the room does factor into this too; I have had algae (not cyano) appear and disappear solely from additional/less daylight in the room.

Byron.