I have had a 36 gallon bowfront with 10 gallon sump for about 4 months now & despite everything including my protien skimmer, clean up crew, and very frequent water changes the hair algae is taking over. I change 50% every two weeks often performing a 10% to 25% change in between. I just switched my salt to a reef specific salt and acclimated a bunch of black mollies from fresh water to salt water to help with algae. My Chaetomorpha in my sump has been very slowy dying with nitrate levels less than 0-40ppm at any given time and a 5500K light on 24/7. Other stats 50lbs live rock branching starburst coral, zoas, porcelain crab, cleaner shrimp, 11 blue & red legged hermit crabs, 2 trochus snails.. with all that being said I did my research. I'm using tap water & that is a big problem for hair algae or so I've read. So I bought a RODI system. The issue is when it gets here and I start my water changes it will be 7 Ph or so I've read & pretty much everything saltwater needs 8 or above. When I add the salt will the Ph go up on its own or do I need a ph booster? Is this the final answer to my algae problem or is there something else I need to be doing? Any tips & advice from those of you with experience will be greatly appriciated!
PH of RODI Water & tackling algae at the source
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lr and sand is the buffer.
bobman
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PH will go up by adding salt you should not have to do anything to raise it and please do not use a PH booster. This is not the final answer to your algae problem as you have been running the tank on tap it ill take a while to get all of the organics and whatever was in the tap water out. 0-40 ppm nitrate is a very wide range from great to algae fuel need to find out why it is swinging so much. Consider organic carbon dosing to help. Are you running a skimmer?
Yes, I'm running a HOB Bak-Pak2 skimmer in the overflow/entrance chamber to my sump. I had a big bloom recently while I was away for 5 days but I also couldn't empty the overflow while I was gone. I'm not feeding anything except twice a week a few flakes hand fed to my cleaner shrimp. All species of crabs & shrimp are molting & I'm not taking the molts out but that's because they eat them & I read that they have a lot of nutrients. Also they have probably molted 2 or 3 times each since I got them so not quite once a month.
DannyB
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Do you have a phosphate test kit? What brand test kit do you use for Nitrates? I would recommend Salifert for this for its accuracy. Try testing both phosphate and nitrate of both your tank water and your tap water. The tap water will tell you how much nutrients you have been dumping in the tank with each water change.
If these numbers are high your rock and sand may have absorbed some of these nutrients, so even with several water changes with RODI the rock and sand may leach these nutrients out for a while, therefore the GHA will still have nutrients to feed off of.
For your question regarding the pH of RODI, If the water is pure enough you could get a pH reading of anything since the water will have nothing in it for a test to give a good reading, but as soon as you add something to the water it will change the pH.
I wouldn't worry about the pH at this stage. If you are concerned it is too low then just add an airstone to your sump and make sure you allow fresh air into the house as often as possible.
If these numbers are high your rock and sand may have absorbed some of these nutrients, so even with several water changes with RODI the rock and sand may leach these nutrients out for a while, therefore the GHA will still have nutrients to feed off of.
For your question regarding the pH of RODI, If the water is pure enough you could get a pH reading of anything since the water will have nothing in it for a test to give a good reading, but as soon as you add something to the water it will change the pH.
I wouldn't worry about the pH at this stage. If you are concerned it is too low then just add an airstone to your sump and make sure you allow fresh air into the house as often as possible.
We have similar setups (36 bow and 5-10 gallon sump). I just had a major GHA outbreak. I believe that some of these things are seasonal due to shifting sun position on windows and changing the ambient lighting in the room of the tank.
What worked for me was Phosban in the HOB supplemental filter, a sea hare, and a 48 hour lights out period. Then I got a toothbrush and knocked loose as much of the remaining GHA I could see on the rocks and a 25% water change. Looking back on the results of the 48 hour blackout, I could have skipped the sea hare, because now I am going to add some nori for him. But he definitely helped.
What worked for me was Phosban in the HOB supplemental filter, a sea hare, and a 48 hour lights out period. Then I got a toothbrush and knocked loose as much of the remaining GHA I could see on the rocks and a 25% water change. Looking back on the results of the 48 hour blackout, I could have skipped the sea hare, because now I am going to add some nori for him. But he definitely helped.
Randy Holmes-Farley
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The pH of top off water has nearly ZERO effect on the tank pH, and you should not assume that even if it is pH 7, that it will lower the tank pH. pH does not have to be impacted in ways that seem logical to nonchemists. 
I discuss that here:
Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-05/rhf/index.htm
from it:
Final Effluent pH
Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:
1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.
2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.
3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).
I discuss that here:
Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-05/rhf/index.htm
from it:
Final Effluent pH
Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:
1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.
2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.
3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).
I use API marine test kit but I only test ph, amonia, nitrite, & nitrate. I always thought phosphates coincide with nitrate levels but I will order a reef specific test kit. Also, algae problem is clearing up. I think the biggest issue was that we were on vacation for a week & not emptying the collection cup on the skimmer. Great articles on RODI! It's all been extremely informative. Thanks guys & gals!
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