Confused by test results....any advice

[DeanoL]

Hi,

Just thought i'd ask for some advice for how to proceed with my latest test results.

Waterbox 90.3 60g tank, have about a 15g sump, redsea skimmer and reefmat.


Results:

• Ph 8.0
• Salinity 1.024
• Ammonia and Nitrite both 0
• Nitrate 5
• Phosphate 0.52 (have always found it difficult to bring phosphate down - have both a PhosZorb bag and PhosGuard in the tank at the moment. Do also have a bag of AquaForest Phosphate Minus handy if needed instead of the PhosGuard/Zorb.
• Alkalinity 5.0/5.3 (used 2 different tests)
• Calcium 320
• Magnesium 1360

I know the alkalinity and calcium is low so I want to bring those up, but I need to lower the phosphate.

I have RODI water ready for a water change if needed to lower the phosphates.

I use aquaforest reef salt.

I also have RedSea Foundation B KH/Alkalinity supplement - should I use some of that? Will that just do alkalinity or also bring up calcium as well?

Thanks for any advice :)

 

[Uncle99]

.5ppm phosphate is on the high end.
I’d consider an LC like say Phosphate X to bring that down to say .2ppm, then GFO down to .1ppm.

You can use multiple brands of media but at .5ppm, that can be expensive.

Go slow…. 0.1 per week say.

The LC in a fine filter sock.

I use two part Red Sea foundation A and B to increase Alk and CA in virtually 1 to 1 ratio.

 

[DeanoL]

.5ppm phosphate is on the high end.
I’d consider an LC like say Phosphate X to bring that down to say .2ppm, then GFO down to .1ppm.

You can use multiple brands of media but at .5ppm, that can be expensive.

Go slow…. 0.1 per week say.

The LC in a fine filter sock.

I use two part Red Sea foundation A and B to increase Alk and CA in virtually 1 to 1 ratio.

Thanks for the reply.

So would you recommend lowering the phosphate first before trying to increase the alkalinity? Is the phosphate the more pressing issue?

 

[Marine Betta]

.5ppm phosphate is on the high end.
I’d consider an LC like say Phosphate X to bring that down to say .2ppm, then GFO down to .1ppm.

You can use multiple brands of media but at .5ppm, that can be expensive.

Go slow…. 0.1 per week say.

The LC in a fine filter sock.

I use two part Red Sea foundation A and B to increase Alk and CA in virtually 1 to 1 ratio.

Thanks for the reply.

So would you recommend lowering the phosphate first before trying to increase the alkalinity? Is the phosphate the more pressing issue?

I agree with what has been said. Was your magnesium lower than this before now? If not, I would reconsider retaking the magnesium. Whenever I see low calcium and alkalinity like that, it normally means magnesium is low. If your magnesium is low, then your calcium and alkalinity won’t increase no matter how much you dose. Do you have corals in the tank now? I would be more concerned about the low alkalinity than the high phosphates. Especially if you have any stony corals. High nutrients are better than low alkalinity, but low alkalinity and low nutrients is a really bad combo. If your magnesium is low, add the magnesium and slowly raise it. If/once that’s magnesium is at least 1250ppm (I like to keep mine at 1440 ppm), you should be able to gradually raise the calcium and alkalinity as you reduce phosphates.

 

[DeanoL]

I agree with what has been said. Was your magnesium lower than this before now? If not, I would reconsider retaking the magnesium. Whenever I see low calcium and alkalinity like that, it normally means magnesium is low. If your magnesium is low, then your calcium and alkalinity won’t increase no matter how much you dose. Do you have corals in the tank now? I would be more concerned about the low alkalinity than the high phosphates. Especially if you have any stony corals. High nutrients are better than low alkalinity, but low alkalinity and low nutrients is a really bad combo. If your magnesium is low, add the magnesium and slowly raise it. If/once that’s magnesium is at least 1250ppm (I like to keep mine at 1440 ppm), you should be able to gradually raise the calcium and alkalinity as you reduce phosphates.

Thanks for the detailed info. To be honest, I haven't really tested magnesium for ages.

Yes I do have corals - mainly sofites and LPS: leather, sinularia, torch, hammer, zoas, blasto, acan, goni, green star polyps, firework clove polyps, desh, trachy. Have a couple small SPS frags on a shelf in there too.

I'll retest the magnesium.

 

[Marine Betta]

I agree with what has been said. Was your magnesium lower than this before now? If not, I would reconsider retaking the magnesium. Whenever I see low calcium and alkalinity like that, it normally means magnesium is low. If your magnesium is low, then your calcium and alkalinity won’t increase no matter how much you dose. Do you have corals in the tank now? I would be more concerned about the low alkalinity than the high phosphates. Especially if you have any stony corals. High nutrients are better than low alkalinity, but low alkalinity and low nutrients is a really bad combo. If your magnesium is low, add the magnesium and slowly raise it. If/once that’s magnesium is at least 1250ppm (I like to keep mine at 1440 ppm), you should be able to gradually raise the calcium and alkalinity as you reduce phosphates.

Thanks for the detailed info. To be honest, I haven't really tested magnesium for ages.

Yes I do have corals - mainly sofites and LPS: leather, sinularia, torch, hammer, zoas, blasto, acan, goni, green star polyps, firework clove polyps, desh, trachy. Have a couple small SPS frags on a shelf in there too.

I'll retest the magnesium.

You’re welcome. Magnesium is very important. Calcium, magnesium, and alkalinity work together to build the calcium carbonate skeletons of corals. Magnesium is kind of like the intermediary between the two and helps keep them in balance and ensures stability. Tidal Gardens has a great YouTube video on the subject if you’re interested. How do your corals look now? Depending on the sps you have, they can be very finicky especially when it comes to alkalinity.

 

[DeanoL]

Just retested - this time I got 1400ppm.

I'm using a RedSea pro kit, it does say it was out of date Nov 2025, not sure if that would make too much of an impact seeing it's only a couple months?

Oh - also remembered I have a duncan and a heap of anenomes (started with just one, but has split a number of times).

Here's a couple of pics - sorry it's so blue.

 

[sdreefer619]

If it were me I would just do a water change every 3 days to get everything in check instead of dosing.

 

[Marine Betta]

Just retested - this time I got 1400ppm.

I'm using a RedSea pro kit, it does say it was out of date Nov 2025, not sure if that would make too much of an impact seeing it's only a couple months?

Oh - also remembered I have a duncan and a heap of anenomes (started with just one, but has split a number of times).

Here's a couple of pics - sorry it's so blue.

Nice tank! All the corals look happy. I’m pleasantly surprised that they look that good given the low alk and calcium, but corals can adapt to unideal conditions. If you retest Ca and Alk, make sure to wash the test vials with RO water before testing again. I’ve gotten weird values before if the sample vials were not properly cleaned. Whether you retest and the values are the same, or feel comfortable with the previous readings, go ahead and slowly increase alk and calcium. Add calcium first then add the alkalinity 15-20 minutes afterwards. If you add them too close together, the calcium will precipitate out. I would make sure that alkalinity is increased slowly. That is one thing you do not want to change too quickly ( I would say no more than 0.5dKh/day but preferably less). Corals hate alk swings. Test again in a day or two and make sure the values are increasing. If you retest and your alk is between 7.5 and 8.1and the calcium is between 420 and 450. You shouldn’t be good, and I wouldn’t dose now. I would test for all of three parameters at least once a week. I would focus on lowering phosphates. Water changes would also help with this. If your magnesium, alkalinity, and calcium are in check, small water changes would be an option. I would err on the side of caution with doing water changes IF your alk is that low. Even if the new water is at the right dKh, a sudden swing could wipe out your corals in the worst case scenario. All corals like stability. Even if you are correcting a subpar parameter, they can die very quickly if it’s a sudden change.

 

[DeanoL]

Nice tank! All the corals look happy. I’m pleasantly surprised that they look that good given the low alk and calcium, but corals can adapt to unideal conditions. If you retest Ca and Alk, make sure to wash the test vials with RO water before testing again. I’ve gotten weird values before if the sample vials were not properly cleaned. Whether you retest and the values are the same, or feel comfortable with the previous readings, go ahead and slowly increase alk and calcium. Add calcium first then add the alkalinity 15-20 minutes afterwards. If you add them too close together, the calcium will precipitate out. I would make sure that alkalinity is increased slowly. That is one thing you do not want to change too quickly ( I would say no more than 0.5dKh/day but preferably less). Corals hate alk swings. Test again in a day or two and make sure the values are increasing. If you retest and your alk is between 7.5 and 8.1and the calcium is between 420 and 450. You shouldn’t be good, and I wouldn’t dose now. I would test for all of three parameters at least once a week. I would focus on lowering phosphates. Water changes would also help with this. If your magnesium, alkalinity, and calcium are in check, small water changes would be an option. I would err on the side of caution with doing water changes IF your alk is that low. Even if the new water is at the right dKh, a sudden swing could wipe out your corals in the worst case scenario. All corals like stability. Even if you are correcting a subpar parameter, they can die very quickly if it’s a sudden change.

Thanks again for such a detailed answer.

I only have the RedSea FoundationB KH/Alkalinity or the Foundatiom Skeletal Elements ABC+

Can I just use the alkalinity one and get a calcium one another day this week?

Or should I use the ABC?

Thanks

 

[Marine Betta]

Nice tank! All the corals look happy. I’m pleasantly surprised that they look that good given the low alk and calcium, but corals can adapt to unideal conditions. If you retest Ca and Alk, make sure to wash the test vials with RO water before testing again. I’ve gotten weird values before if the sample vials were not properly cleaned. Whether you retest and the values are the same, or feel comfortable with the previous readings, go ahead and slowly increase alk and calcium. Add calcium first then add the alkalinity 15-20 minutes afterwards. If you add them too close together, the calcium will precipitate out. I would make sure that alkalinity is increased slowly. That is one thing you do not want to change too quickly ( I would say no more than 0.5dKh/day but preferably less). Corals hate alk swings. Test again in a day or two and make sure the values are increasing. If you retest and your alk is between 7.5 and 8.1and the calcium is between 420 and 450. You shouldn’t be good, and I wouldn’t dose now. I would test for all of three parameters at least once a week. I would focus on lowering phosphates. Water changes would also help with this. If your magnesium, alkalinity, and calcium are in check, small water changes would be an option. I would err on the side of caution with doing water changes IF your alk is that low. Even if the new water is at the right dKh, a sudden swing could wipe out your corals in the worst case scenario. All corals like stability. Even if you are correcting a subpar parameter, they can die very quickly if it’s a sudden change.

Thanks again for such a detailed answer.

I only have the RedSea FoundationB KH/Alkalinity or the Foundatiom Skeletal Elements ABC+

Can I just use the alkalinity one and get a calcium one another day this week?

Or should I use the ABC?

Thanks

You could dose with just Foundation B for now, but increasing alkalinity alone can lower Calcium levels. It’s a seesaw effect but magnesium stabilizes everything. You can purchase all three together in 250 mL bottles. That’s probably the best bang for your buck. I would encourage you, if you haven’t already, to get your lfs to check your alkalinity and calcium to rule out faulty tests and to make sure you really do need to increase these values since your coral looks good. Out of curiosity, when was your last water change, did you test afterwards to make sure all your parameters were on point, or is there something wrong in the tank that you thought could be related to water quality? When you did the last change, I doubt the dKh of the new water was 5, and your coral would probably have had a negative reaction to such a large swing. Your sps would almost definitely be having a bad time. If you go the water change route, I would match the alkalinity to the number that’s the target for that day.

 

[DeanoL]

I did a water change 5 days ago. Tested the phosphate 4 has later and it was 0.38. But didnt test alkalinity as it was high phosphate I was targeting.

This morning I had a fair bit of time so thought I'd test everything, they are the results above.

I did just do a 30L (about 10%) water change and will do another during the week. Ill add some Foundation B now but will get some of all of them from the LFS this week.

I'll try take some water in to them at the same time for them to test alkalinity and calcium.

Thanks again for all your input

 

[ReneReef]

Before your start adding:
I recommend correcting your salinity first. Its a bit low. Increasing salinity will increase Ca and Alk a bit as well.
The specific gravity of ocean waters is 1.0264.

I do NOT recommend using the Red Sea additives!
First, it is soda ash based and it is not recommended to use that for large alk adjustments.
Second, it is very expensive and not worth the extra cost. Its 3 to 4 times as expensive as other big brands and more than 10 times as expensive as using baking soda and calciumchloride.

Regarding your phosphate.
Looking at the pictures of your tank, I wouldn’t worry and just keep it from rising further.

 

[DeanoL]

Before your start adding:
I recommend correcting your salinity first. Its a bit low. Increasing salinity will increase Ca and Alk a bit as well.
The specific gravity of ocean waters is 1.0264.

I do NOT recommend using the Red Sea additives!
First, it is soda ash based and it is not recommended to use that for large alk adjustments.
Second, it is very expensive and not worth the extra cost. Its 3 to 4 times as expensive as other big brands and more than 10 times as expensive as using baking soda and calciumchloride.

Regarding your phosphate.
Looking at the pictures of your tank, I wouldn’t worry and just keep it from rising further.

Good to know about the salinity. Ill try and increase it slowly over next week.

I did add some of the Foundation B already though. Only 10ml which should raise alkalinity about 0.3dkh (1ml per 25gal does 0.1dkh and I have 75 gal including sump).

There's a fair bit left in the bottle so id hate to waste it. But out of curiosity is there a different brand you'd recommend?

Thanks also for the info about the phosphate. I wont stress as much about it but if I can bring it down slowly I'll try. Just thinking if I can bring down phosphates it might help with some algae.

 

[mcarroll]

just to pile on...your phosphates aren't hurting anything, but it would be worth sorting out why they aren't being used up. (I wonder if you have lower nitrate levels than you think? ...only one potential explanation, but it is a common one). In the short run, I would stop doing what you are doing to lower phosphate levels.

Mineral levels seem low across the board so I agree this may just be a salinity issue. Fix your salinity.

But I would also test mineral levels on your next freshly mixed batch of seawater to check what you're putting in the tank during water changes. Your tank's numbers will trend towards the numbers of the freshly mixed seawater.... and if those values are low for some reason, you get the picture.

 

[DeanoL]

Ok will work on increasing salinity and will test the next batch of water i mix up.

Thanks for the suggestions everyone

 

[slingfox]

Agreed with the above that you need to doublecheck your salinity. Specifically, what are you using to measure salinity? Search on this board for Ramsay Holmes Farley’s instruction on how to make DIY calibration fluid.

If you are using a cheapo refractometer it is wet likely your salinity is too low. This is an issue that comes up constantly on Reef2Reef.

 

[ReneReef]

Good to know about the salinity. Ill try and increase it slowly over next week.

I did add some of the Foundation B already though. Only 10ml which should raise alkalinity about 0.3dkh (1ml per 25gal does 0.1dkh and I have 75 gal including sump).

There's a fair bit left in the bottle so id hate to waste it. But out of curiosity is there a different brand you'd recommend?

Thanks also for the info about the phosphate. I wont stress as much about it but if I can bring it down slowly I'll try. Just thinking if I can bring down phosphates it might help with some algae.

Of course if you already have it, use it.
The added 10 mL will add a bit more than 0.3 dKH.
Your net system volume will be less than 75g, your rocks and sand are not water. Also the 1 mL per 25 gallons raising alk by 0.1 is a rough conversion from Liters to gallons. It will be slightly more.
I estimate your net system volume is about 60g and the 10 mL of foundation B to raise alk by 0.4.

I’m not familiar enough with US pricing of brands/products to recommend one.
But for simple incidental corrections like these I always recommend baking soda and calcium chloride.
Randy Holmes Farley has all the info you need on the reef chemistry part of this forum.

I’d estimate your tank does not consume much KH/calcium/etc. daily. Then Tropic Marin All for Reef is an easy to use all in one product. When you buy it in powder form it is also quite cost effective.

Algae issues are not a phosphate problem, but a grazing problem. Lack of grazing that is.

 

[Marine Betta]

I did a water change 5 days ago. Tested the phosphate 4 has later and it was 0.38. But didnt test alkalinity as it was high phosphate I was targeting.

This morning I had a fair bit of time so thought I'd test everything, they are the results above.

I did just do a 30L (about 10%) water change and will do another during the week. Ill add some Foundation B now but will get some of all of them from the LFS this week.

I'll try take some water in to them at the same time for them to test alkalinity and calcium.

Thanks again for all your input

You’re welcome. The others have given you good advice too! Besides the brands listed, you can look into brightwell and aquaforest for Ca,Alk, and Mg supplements. I would pay attention to the ion composition and guaranteed analysis of whatever supplement you use. Increasing your salinity will raise your Ca, Alk, and Mg, but it likely won’t raise them to the desired target values, and you will need to supplement afterwards. As for the phosphates, once your Ca, Alk, and Mg are higher, your coral will start growing faster and will consume nutrients (nitrates and phosphates). Your phosphates are probably high now because they’re not really being used by the coral. They should start coming down naturally when the coral consumes them. Regarding nitrates, 5 ppm is ok, but it’s on the low side for a mixed reef. You may want to consider increasing it to 10-15 ppm. When your coral starts growing more, you will have to keep an eye on the nitrates and ensure they don’t bottom out. You can raise nitrates by feeding your fish more. This will likely raise phosphates, but your fish will be happy with you. The other option is to dose nitrates. Don’t worry about the nitrates now though. I would raise the salinity, and then continue dosing as needed. You can worry about the nutrient levels once everything is stable.

Like everyone said, Randy Holmes-Farley is an expert on reef chemistry, so he is a great source of information on this topic.

 

[DeanoL]

Agreed with the above that you need to doublecheck your salinity. Specifically, what are you using to measure salinity? Search on this board for Ramsay Holmes Farley’s instruction on how to make DIY calibration fluid.

If you are using a cheapo refractometer it is wet likely your salinity is too low. This is an issue that comes up constantly on Reef2Reef.

I have a portable refractometer, i cant see a brand but the box says RHS-10 on the top right.

I have never calibrated it, but the LFS i bought the aquarium, sand, rocks, everything from came to my house and set it all up and showed me how to use it and didn't tell me about calibration. I am assuming they did it when they set it up.