Post algae bloom steps

Hi everyone,

We have a 280 litre tropical tank with Tetras, Danios, Anglefish, a Red Torpedo, zero real plants, and several rocks of varying size (whose type escapes me, but I know they produce lime).

Several weeks ago we had a bad algae bloom (see before and after photos). We tried many different things to resolve it - mass water changes, high doses of API Algaefix, no water changes, leaving the light off for a week, adding a carbon filter to the biological filter - without success. We were advised by a local retailer to stop using Sera Bio Nitrivec (something we added religiously during water changes for many years). We were also advised by another local retailer to use a Pond One UV Stabiliser which finally did the trick. It took about 4 days for the green cloud to turn into a white cloud which was subsequently removed over the following week or two with water changes.

We lost no fish during the bloom or the treatment phase, and things seem to have settled down now, so we have some questions for the community:

1. What things do we need to do post bloom to ensure it doesn’t happen again?
2. Should we start to add the Nitrivec at water changes again, or is it optional?
3. We still have some surface algae (on the rocks, glass, etc). Is this cause for concern?
4. Although it's hard to see in the 'after' photo, there is still a mild milkiness to the water. Again, is this cause for concern?

Kind regards,
Michael.

A few observations that should help. And to begin with...in the absence of live plants, algae has a tremendous advantage. Any aquarium will provide nutrients from the feeding of the fish. With no plants, algae will use these nutrients. Light will be present at whatever level from ambient room light (daylight) or tank light, or both. Algae can use any light, it is not as fussy as higher plants when it comes to light intensity or spectrum. So you will have algae because it is part of the natural world in such cases.

Green water is caused by unicellular algae. This is the one and only form of "algae" that UV can deal with at least in part. This is pone option going forward, and it should keep unicellular algae in check somewhat. However, it will be much easier to also deal with the underlying issue, and that is nutrients and light.

Fed minimally; most of us at least initially listen to the nonsense from food manufacturers about fish needing to be fed several times a day. Except for fry, this is pure rubbish. Once a day--and only what they actually require--and having one, two or evn three "fast" days is not a problem for mature (as opposed to fry) fish. Second, do good tank maintenance. Regular water changes of 50-70%, meaning once a week, with a good vacuum of the substrate. Keeping the filter clean--all that brown gunk is organic nutrients. Live plants really help, and floaters are the best here because they grow rapidly (thus using more nutrients) and provide shade. Substantial floating plants, like Water Sprite, Water Lettuce, Tropical Frogbit are ideal; smaller plants will help too but obviously not as much.

Never, never, never use algicides. Chemicals in the water have the possibility/probability of entering the fish's bloodstream with the water via osmosis continually, and substances that are not absolutely essential for fish survival pose more of a risk than benefit.

Nitrivek--throw it out. The claims it makes are highly skeptical, and you want the natural biological processes to work and they do not need help from more questionable substances. I don't know what species of "bacteria" this supposedly contains, but it is more of a sales hype than actual help. Regular balance and maintenance is the method for a healthy aquarium, not adding chemicals/substances that mess with these.

Thanks so much for your detailed response! The problem is we suck at live plants. We've tried sooo many times to have them in our tank and they all die. In fact we believe that the cause of the bloom was the last attempt to have live plants in the tank. However, with more research and assistance from this excellent forum, we'll get it right. For example, never considered floating plants.

Thanks again!

Floating plants are the easiest. They are under the light so get plenty of that. They have the aerial advantage, in that the floating leaves can assimilate CO2 from the air rather than water, and this (air) is four times faster for the plant so they get a lot. You may need a liquid comprehensive fertilizer to ensure they have all nutrients needed. But floaters not only remove incredible levels of ammonia, they provide shade which fish enjoy, and they will keep algae under control.

Water Sprite is probably the best for all this.