Salinity adjustment

[Lynnzer]

Over the few months I've had a marine tank I thought I'd learned a good deal. Seems like I am wrong.
Most of the frags I bought have withered with a few exceptions and I've even lost the odd fish for no apparent reason.
The water parameters, Ammonia, Nitrite and Nitrate are at zero or near enough not to matter. The ph is somewhere around 7.8 so I thought everything was OK. However I became aware of the need to check salinity and was horrified at seeing the level at around 1.32. I didn't even think there was a check for that.
So I'm now trying to drop the level to as near as 1.25 as possible and have had to use rainwater to do it with. I used the same rainwater to add to my freshwater tanks and never had a problem so I guess it should be OK in a marine tank. Some will say don't do it, however I had little chance to get RO for a couple of weeks.
It seemed to work as the reading is now slightly below 1.030 but I seem to have put one heck of a lot of rainwater in to achieve it.
Is there a chart showing the percentage replacement volumes to drop the readings that I can refer to?

 

[afrokobe]

You cant just add rainwater as water will get evaporated and the salinity will come back to the same. The amount of salt in the water stays the same unless you took some of the initial salt water out. I would do some water changes with lower salinity to offset some of the salinity shock. I would also advise RODI not just ro water.

 

[Cell]

Gonna be a tough hobby for you if you cannot access RO water for weeks at a time. Rainwater is not clean. It's not going to be good long term for your livestock.

 

[Nman]

Get your salinity down slowly then when your at1.025 salinity get your self an auto top up you can make one out of a juice bottle and two bits of air pipe try looking on YouTube diy auto top up . This will keep your salinity stable. You should invest in a ro takes all the rubbish out of your tap water don’t use rain water as said above

 

[Lynnzer]

I have a new D D 900 tank with sump and ATO coming this next week so that tank will be fine. However the tank I'm asking about right now doesn't have a sump, and an ATO relying on gravity would need the bottle at a height above the tank. I can't do that. I don't have room and in any case it would look ugly on the wall above the tank. Problem is that the "wall" is actually a window anyway.
Is there an ATO that will pump water up from below the tank level?
I have a spare pump I could use with a lift height of 2m

 

[Nman]

Yes get a auto top up and some sort of container to hold your fresh water that pump it up when needed . I wouldn’t worry about something looking ugly for now as long as the water in your tank is stable and you will have less problems in the long run . Her is my gravity fed diy and I don’t need to think about salinity anymore. Maybe not the best looking but keeps my salinity bang on

 

[Lynnzer]

I got it sorted. I had an auto top off already for new tank that's on the way so took a look at that and put it in the tank I have now. It works like ..... well ..... what it says on the box. I had a spare tank that I placed in the cabinet and set things up. It's just the job.
I've now changed sufficient water to reduce the salinity to acceptable readings so that's one thing off my mind. Thanks for the responses

 

[Cell]

Now about that RODI...you honestly might be better off using dechlorinated tap water vs rain water.