So a year down the track after building my algae reactor I've given up using it due to poor results. In the mean time I've tried a few other things to get my phos levels down...
Growth was not as good as I would have liked with the algae reactor and in all honesty it could not compete with the display. So I decommissioned the algae reactor and filled it up with PhosGuard. The PhosGuard was better, but it was an expensive solution. I then tried GFO in the hope that it would last longer / be better than the PhosGuard but again, it did little to the levels and was expensive to maintain.
Right about the time of Covid my roll filter decided to strip a gear which put it out of action. This meant that I had to stop using the GFO as I had no way to take the fine particles out of the water, so my tank essential was left to go fallow. I ended up with a LOT of algae in the display tank. I was too embarrassed to take a photo.
So when the replacement part finally arrived (two weeks ago) the tank had lain fallow for six months. Fortunately the algae was pretty easy to remove, it just lifted out. I ended up with a half a bucket.
So what to do about this phosphate issue?
I decided to use Lanthanum Chloride. I had read about this last year when I researched the algae reactor, but general consensus was that it was too dangerous to use. Of course, such advice is usually just anecdotal. More recently I ended up reading a few articles where people were successfully using it as part of their tank regimen with no issues. I also read about a fella who had used Hy-Chlor - a readily available pool cleaning chemical here in South Australia. Preferring DIY solutions for tank husbandry this seemed just the ticket.
So after a trip to our local DIY shop I ended up with a litre bottle of Hy-Chlor for the paltry sum of AU$30. I mixed up a solution of 1ml of hy-chlor to 1 litre of RO water and made a crude drip doser and then dosed the tank over an 8 hour period. I measured the phos levels the next day, the level had halved.
I left the tank for a day. Further dosing using half of the amount (0.5ml in 1/2 litre) saw my levels drop to just over zero.
That's the lowest the Phos level has been since I started measuring it
I left the tank for a few days. Measuring the phos levels again saw them rise, which is completely expected as the phos will be leaching back out of the rock and substrate. One thread I read had a tank owner saying that it had taken over a year to get this leaching under control, so I expect that I have a long journey ahead. The great thing is that the chemical is dirt cheap ($30 for a litre) and so will last a LOOOOONG time.
Next step is to set up some kind of dosing setup. I do however need to exercise some caution and get a test kit so that I can also test for free LaCl3 in the water. Eventually when the phos has depleted the free LaCl3 levels will rise in the water column, if this level is allowed to rise too high it will become lethal to the tank. The highest safe concentration documented is 1mg/l, which is a massively high amount compared to the amount I'm dosing, but if left unchecked, especially if auto dosing the stuff, it could soon build up.
Other users use a higher dose periodically to bring the phos levels down and then let them rise up again. I'm not sure if this is the best option for me with the leeching LR. What I want to try and do is match the dosing rate to the leeching rate so that it does not bring the phos down to zero but some small value instead. This way I should be able to detect when the leeching has subsided as the phos levels will then drop to zero. Well that's the theory at any rate.
In summary, LaCl3 does not appear to be as dangerous or difficult to use as many have made it sound. Just use dilute amounts, over a period of time interspaced with phosphate testing and you will be fine. The results I have seen are very promising and I feel that as long as I test the free LaCl3 in the water column I cannot see why it should be an issue.
If you do use this method you will need a fine (10 micron) filter setup to remove the flocculant from the water (LaCL3 bonds with the phosphate to turn it into a solid that needs to be removed by filtration). I dose into my weir, which goes directly to my roll filter, this gives a fair amount of reaction time without the LaCl3 reaching the tank. It's quite satisfying to watch the roll filter going crazy as the LaCl3 is dosed. Others place a filter sock in a high flow area in their sump and dose into that instead. Whatever method you use it seems that general consensus is to try and catch the flocculant and prevent it from going into the tank as it can irritate some fish. This is evidently more prevalent with tangs, however I have a blue tang in my tank which has not been bothered at all. Maybe this is related to the small dose, so there is less free LaCl3 in the water column.
Some details on my dosing
I'm using Hy-Chlor pool phosphate remover - it's AU$30 for 1 litre - https://www.bunnings.com.au/hy-clor-1l-pool-phosphate-remover_p3090143 It's essentially pure LaCl3 diluted in solution. There are no other chemicals noted in the 'ingredients'
Hy-Chor contains a concentration of 150mg/litre of LaCl3
I diluted it at a ratio of 1ml into a litre of RO water
This brings the actual concentration down to 0.15mg/litre
This is then dosed into my system which is 233 litres over about 12 hours. (some dose this amount much quicker but I prefer to err on the side of caution)
This means that the actual concentration in my tank is potentially as high as 0.00064mg/litre assuming that none of it gets consumed by phosphate and it stays in it's initial state. Of course the LaCl3 is consumed and precipitated out as a solid which further reduces the amount of free LaCl in the tank.
To get to dangerous HcLa3 levels (assuming the 1mg / litre threshold) it would take me 1553.5 litres of this solution to bring the LaCl3 level in the tank up to 1mg/litre.
That means there's lots of room for raising the dosing strength, but given I have seen promising results from the small dose I have been using I will stick with the current regimen. There is also the phosphate level itself to consider, it dropped down to near zero levels with the testing that I undertook, a higher dosing level / rate would strip the phosphate level too low which would not be good for the tank as some trace levels of phosphate are required for the corals. Likewise too high a dose of LaCl3 will leave unreacted LaCl3 free to enter into the display, where it will be free to bond with phosphate sources there. This would probably result in flocculant being created on the surface of the live rick and substrate as the phosphate leeches out. This flocculant would then be free to float around and may irritate tank inhabitants as previously described.
I'll get it set up and do some further testing and then report back here after a period of time with how things are going. Hopefully it will be some positive news