When tests read ZERO, yet algae abound...why aren't corals happy?

[IPWitan]

So when phosphates and nitrates are measured at zero, but there is bubble algae, then the tank clearly has some phosphate and nitrates or it wouldn't grow. The theory is that the nitrates/phosphates are coming from the rocks and the algae grabs it before it makes it to the water column. ...or something else. But if the free phosphates and nitrates are zero, then why aren't the corals happy? Is the tank too clean for coral, but perfect for bubble algae?

When someone reports algae, the common recommendation is to do water changes to bring the nitrates/phosphates down. But the tests read zero... How would phosphates and nitrates be REDUCED by a water change?

I had this thought that if film algae develops on the sand or rock, it would effectively suffocate the critters living under the algae. As the critters/bacteria die, it feeds the algae. This is probably bad. Clearly removing algae is a nutrient export, so that is probably good.

Maybe I am pleading for someone to explain in greater detail how a water change would positively affect an algae problem where tests read no phosphates and nitrates. And similarly, why having algae is BAD for corals, if they are consuming all nitrates and phosphates. If doing water changes pulls out stuff and adds new and different stuff, and we don't really know what is going it or out, or why that it is good, but it seems to make things good, then we need to at least be honest about...

 

[cilyjr]

Well I don't think of algae as bad for nutrient export. It's unsightly for most people in display tanks but it's simple to say bad.

Turf algae scrubbers are great examples of people intentionally growing "nuisance" algae from nutrient export

 

[jah-hoeva]

Also depending on the types of coral you have, you water can be too clean. My tank is primarily LPS. When I had undetectable phosphate and nitrate, my corals were not the happiest.

 

[RMc]

I think Jah-hoeva is hitting the nail on the head. When we see algae starting to take over, our first reaction is to work on dropping our nutrients to zero. The problem is that when algae is well established it will outcompete most coral for any available nutrients. There can be other limiting factors as well. If for some reason the tank husbandry / chemistry favors algae over coral - the coral will continue to lose the battle against the algae.

Some examples of husbandry/chemistry that favors algae:
-Long photo periods (10 hours or more beings to favor algae over coral)
-Light level is too high or too low (When light is outside of the optimal level for coral, it may favor algae which is more forgiving)
-Red spectrum (red light spectrum favors algae over coral)
-Flow (sub optimal flow will favor algae over coral)
-Pockets of detritus or nutrients (concentrated piles of nutrients will favor algae growth)
-Sub optimal Alk/CA - when ALK/CA is either above or below the optimal level for coral growth, algae may more readily take up NPK than coral
-Low bacterial cultures - Low levels of nitrifying/denitrifying bacteria may favor more algae growth over coral as many coral will consume the bacteria
-High Iron - Iron promotes algae growth, but also contributes to coral growth and green coloration. Excess Iron may be an issue.
-Low levels of macro nutrients such as Amino acids in the WC. Though coral and algae may take up amino acids, it seems that during lights on coral will take it up faster. Low levels of these macro nutrient (through feeding less fish food) may contribute to happier algae than coral.

 

[IPWitan]

Thank you for the long list. That is very helpful. So I am right - sort of - that a tank can be ULN while at the same time have an over population of algae in the display - at least from the corals uptake perspective. So, if you have nuisance algae in the display, and you want it gone, one should really find a way to remove the algae - usually by using manual removal or critter removal (snails, hermits, fish, which is removed via poop and skimming thereof). I think ULN needs to be redfined... The other option, or both, is to create another location which consumes faster than the display, e.g. refugium or scrubber. If one simply does water changes without removal, then algae should grow and take over, eventually. If the water is testing positive for nitrates and phosphates, then water changes can make a reduction.

I think for me, my tank was going great until the emerald crabs died. Thereafter bubble algae took over. This caused coral stress due to being out competed for nitrates. As corals stopped growing, started dyng, and uptake reduced drastically, causing spikes in alk.

*Of course having my salinity completely out of wake for say, forever, didn't help.